STATE OF SEBASTIAN INLET REPORT 2014 -...
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i STATE OF SEBASTIAN INLET REPORT 2014 An Assessment of Inlet Morphologic Processes, Shoreline Changes, Sediment Budget and Beach Fill Performance By Gary A. Zarillo, Irene M. Watts, Leaf Erickson, Florian Brehin, Kristen L. Hall, Satyam N. Chauhan Department of Marine and Environmental Systems Florida Institute of Technology 150 University Blvd. Melbourne, FL 32901
Transcript of STATE OF SEBASTIAN INLET REPORT 2014 -...
i
STATE OF SEBASTIAN INLET REPORT
2014
An Assessment of Inlet Morphologic Processes, Shoreline Changes,
Sediment Budget and Beach Fill Performance
By
Gary A. Zarillo, Irene M. Watts, Leaf Erickson, Florian Brehin, Kristen L. Hall, Satyam N. Chauhan
Department of Marine and Environmental Systems
Florida Institute of Technology
150 University Blvd.
Melbourne, FL 32901
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Executive Summary
The annual update of the State of Sebastian Inlet includes six major areas of work; 1) an
update of the analysis of volume contained in the inlet sand reservoirs, 2) analysis of
morphologic changes within the inlet system, 3) analysis of the sand budget based on the results
of the sand volume analysis, 4) an update of the shoreline change analysis, 5) a numerical
modeling analysis Coconut Point erosion, and 6) a description of the Sebastian Inlet District GIS
database.
The sand volumetric analysis includes the major sand reservoirs within the immediate
inlet system and sand volumes within the extended sand budget cells to the north and south of
Sebastian Inlet. The volume analysis for each inlet sand reservoir extends from 2004 to 2014.
Similar to the volumetric analysis described in previous state of the inlet reports, most inlet sand
reservoirs are in a long-term dynamic equilibrium characterized by occasional large seasonal
changes in volume superimposed on longer term trends of a lower order of magnitude. An
example of this is the volume history of the Sebastian Inlet flood shoal, which has undergone
little net volume change between 2004 and 2014, but can experience seasonal variations that
exceed 50,000 cubic yards.
The most noticeable shift in the flood shoal volume is a decrease of about 200,000 cubic
yards between 2011 and 2014. This change is considered to be temporary and due to excavation
and expansion of the sand trap in winter-spring of 2012 and 2014, which effectively cuts off the
sediment supply to the flood shoal. An additional factor is loss of sea grass beds in 2011, which
caused increased erosion over the flood shoal surface. Likewise, the Sebastian Inlet ebb shoal has
experienced gradual net gain in volume since 2004 along with larger seasonal variations in
volume that include occasional sand volume gains and losses in a range of 50,000 to 100,000
cubic yards. In the period of 2012 to 2014, the ebb shoal has increased in volume by about
35,000 cubic yards, whereas the lower ebb shoal has increased in volume by about 50,000 cubic
yards. In addition to sand that can temporarily accumulate from the inlet, some additional
volume may be added from sand backpassing from recent beach fill projects that were competed
in the 2013 to 2014 period
The dynamic equilibrium of sand reservoirs associated with Sebastian Inlet is also
reflected in sediment budget calculations. Whereas net changes in sediment budget cells,
including the cell that contains Sebastian Inlet sand reservoirs, are relatively small over a 20-year
period, seasonal changes in any of the cells can occasional exceed 100,000 cubic yards. In this
report the sand budget for the Sebastian Inlet region is reported at several different time scales,
including longer time scales of 5 to 10 years and shorter time scales of 2 years. Over the time
period of 2005-2014 the sand budget cell that includes all sand reservoirs associated with the
inlet have retained very little sand. When comparing winter to winter sand budgets in the 2004 to
2014 period the inlet area has retained an annual average of about 8,000 cubic yards
Similar to the sand volume analysis, the results of shoreline mapping from survey data
vary considerably by time scale. Over the 10-year time scale from 2004 to 2014, shoreline
changes south of the inlet reflected the position of beach fill placement in 2007, 2011, 2012 and
2014 These projects provided sections of advancing or stable shoreline. An areas of shoreline
recession over this time period between FDEP R-markers of about R8 and R17 could be
interpreted as lateral dispersion of beach fill material in this area.
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The section of beach 5,000 feet north of Sebastian Inlet during the summer 2004 to
summer 2014 period was subject to shoreline recession. Variable, but small net shoreline
changes occurred to the north. Over the 2004 to 2014 period the sand budget analysis indicates
loss of sand volume, but at a relatively small magnitude on an annual average basis. At the
intermediate time scale of 2009 to 2014 most of the shoreline for 15,000 feet north of the inlet
was stable or advanced. Average annual sand volume changes in this areas were negative but
relatively small. On the shortest time scales, shoreline change and change rates were spatially
variable and largely reflect seasonal beach conditions, as well as fill placement in the 2012-2014
period.
The Sebastian Inlet Coastal Processes Model was modified to include high resolution
computational cells along the interior of the main inlet conveyance channel. After verifying that
the model produced good results for the existing conditions, a series of model tests were
conducted to evaluate shore protection methods. Model tests were performed that include various
configurations of groins and breakwaters designed to reduce wave and current energy and to
accumulate sand along the eroding shoreline. Additional model tests were run to evaluate the
performance of coarse texture beach fills. Model results showed that groin and breakwater
structures may protect the shoreline from erosion, but would alter the natural sand supply and
potentially result in filling of a navigational channel beyond the southwest end of the point. A
recommendation is made to maintain the natural sediment budget and add a coarse grain fill that
would resist erosion from currents and wave action along the coconut point shoreline.
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Table of Contents
Executive Summary ........................................................................................................................ ii
Table of Contents ........................................................................................................................... iv
List of Tables .................................................................................................................................. x
1.0 Introduction and Previous Work ............................................................................................... 1
2.0 Sand Volume Analysis Methods............................................................................................... 1
3.0 Sand Volume Analysis Results ................................................................................................. 4
3.1 Individual Inlet Reservoirs .................................................................................................... 5
3.2 Sand Budget Cells ............................................................................................................... 12
4.0 Bathymetric and Morphologic Change ................................................................................... 17
4.1 Methods............................................................................................................................... 17
4.2 Seasonal Changes: 2013-2014 ............................................................................................ 17
5.0 Sand Budget Update 2012: Methods ...................................................................................... 22
5.1 Sand Budget Results ........................................................................................................... 24
Short-term Sand Budget ........................................................................................................ 26
6.0 Shoreline Changes .................................................................................................................. 28
6.1 Methods............................................................................................................................... 28
6.2 Shoreline Changes from Aerial Imagery Historical Period (1958-2014) ........................... 30
6.3 Ten-Year Period (2004-2014) ............................................................................................. 34
6.4 Latest Update (2009-2014) ................................................................................................. 36
6.5 Latest Update (2013-2014) ................................................................................................. 37
7.0 Survey-Based Shoreline Analysis ........................................................................................... 64
7.1 Methods............................................................................................................................... 64
Short Term Seasonal Changes .............................................................................................. 64
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Long Term Shoreline Changes.............................................................................................. 68
8.0 Hydrodynamic and Morphodynamic Numerical Modeling .................................................... 74
8.1 Introduction ......................................................................................................................... 74
8.2 Coconut Point Site Characterization ................................................................................... 74
8.3 Model Development............................................................................................................ 78
8.4 Hydrodynamic Characterization ......................................................................................... 81
Waves .................................................................................................................................... 81
Currents ................................................................................................................................ 82
Observed Morphologic Evolution of Coconut Point ............................................................ 83
Calculated Sediment Transport Pathways and Morphologic Evolution .............................. 85
8.5 Coconut Point Alternatives ................................................................................................. 87
Design Considerations .......................................................................................................... 87
Alternative Results .............................................................................................................. 100
8.6 Conclusion and Recommendations: Coconut Point Restoration ...................................... 113
9.0 Geographic Information Systems ......................................................................................... 115
9.1 Sebastian Inlet Data Management .................................................................................... 115
9.3 ArcGIS Spatial analysis .................................................................................................... 117
10.0 References ........................................................................................................................... 121
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List of Figures
Figure 1. Extent of hydrographic survey (2014 summer). .............................................................. 2
Figure 2. Morphologic features forming the inlet system reservoir. ............................................. 4
Figure 3. Sand budget cells. Note the inlet cell does include the flood shoal. ............................... 5
Figure 4. Volumetric evolution of the ebb shoal from summer 2004 to summer 2014. ................. 6
Figure 5. Volumetric evolution of the outer ebb shoal from summer 2004 to summer 2012. ....... 6
Figure 6. Volumetric evolution of the attachment bar from summer 2004 to summer 2012. ........ 8
Figure 7. Volumetric evolution of the south fillet from summer 2004 to summer 2014. ............... 8
Figure 8. Volumetric evolution of the south beach from summer 2004 to summer 2012. ............. 9
Figure 9. Volumetric evolution of the north jetty fillet from summer 2004 to summer 2014. ..... 10
Figure 10. Volumetric evolution of the upper north fillet from summer 2004 to summer 2014. . 10
Figure 11. Volumetric evolution of the sand trap from summer 2004 to summer 2014. ............. 11
Figure 12. Volumetric evolution of the flood shoal from summer 2004 to summer 2014. .......... 12
Figure 13. Recent volumetric evolution of the N2 sand budget cell. ........................................... 14
Figure 14. Recent volumetric evolution of the N1 sand budget cell. ........................................... 14
Figure 15. Recent volumetric evolution of the Inlet sand budget cell. ......................................... 15
Figure 16. Recent volumetric evolution of the S1 sand budget cell. ............................................ 16
Figure 17. Recent volumetric evolution of the S2 sand budget cell. ............................................ 17
Figure 18. Net topographic changes from summer 2013 to winter 2014. .................................... 18
Figure 19. Details of net topographic changes from summer 2013 to winter 2014. ..................... 19
Figure 20. Net topographic changes from winter 2014 to summer 2014. .................................... 20
Figure 21. Details of net topographic changes from winter 2014 to summer 2014. ..................... 21
Figure 22. Net topographic changes from summer 2013 to summer 2014. .................................. 21
Figure 23. Details of net topographic changes from summer 2013 to summer 2014. .................. 22
Figure 24. Schematics of a littoral sediment budget analysis (from Rosati and Kraus, 1999). .... 23
Figure 25. Change (ft.) in shoreline positions, 1958-2014. .......................................................... 33
Figure 26. Change (ft.) shoreline positions, 1958-2013. .............................................................. 35
Figure 27. Change in shoreline position, 2009-2014. ................................................................... 36
Figure 28. Change (ft.) in shoreline position, 2008-20134 .......................................................... 38
Figure 29. Survey-based shoreline change from summer 2013 to winter 2014. .......................... 65
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Figure 30. Survey-based shoreline change from winter 2014 to summer 2014. .......................... 66
Figure 31. Survey-based shoreline change from summer 2013 to summer 2014. ........................ 67
Figure 32 Survey-based shoreline change from winter 2013 to winter 2014. .............................. 67
Figure 33 Survey-based shoreline change from summer 2009 to summer 2014. ......................... 69
Figure 34 Survey-based shoreline change from summer 2005 to summer 2014. ......................... 69
Figure 35 Survey-based shoreline change from summer 2005 to summer 2014. ......................... 70
Figure 36 Survey-based shoreline change from summer 2009 to summer 2014 .......................... 71
Figure 37. Comparison of aerial vs. survey based shoreline position for summer 2013 (North
domain). ........................................................................................................................................ 72
Figure 38. Comparison of aerial vs. survey based shoreline position for summer 2013 (South
domain). ........................................................................................................................................ 72
Figure 39. Image-based vs. image-based shoreline comparison................................................... 73
Figure 40. Fine Grained Material on Coconut Point (Panel a, left) Facing due East; (Panel b,
right) Fine grained material and exposed concrete blocks on eastern end of construction area. .. 75
Figure 41. Exposure of Concrete Blocks and Erosion of Shoreline (Panel a, left) Facing due
West; (Panel b, right) Facing due North East ............................................................................... 75
Figure 42. Plastic Cellular Material Exposure (Panel a, left) Field Photo facing due West; (Panel
b, right) Facing due West. ............................................................................................................. 76
Figure 43. Shoreline erosion at interface between concrete block and plastic cell material. ....... 77
Figure 44. Google Earth Aerial Image, (Panel a, left); Rubble Mound Depression (Panel b, right).
....................................................................................................................................................... 77
Figure 45. Coconut Point Construction Materials (Google Earth, 2014). .................................... 78
Figure 46. CMS components (CIRP, 2014). ................................................................................. 79
Figure 47. (Panel a, left) Grid refinement around Coconut Point with aerial imagery (panel b,
right) depth contours around Coconut Point (aerial imagery: Google Earth, 2014). .................... 80
Figure 48. Topography Dataset Coverage. ................................................................................... 81
Figure 49. Calculated Wave Height and Vectors with Wave Rose inset. ..................................... 82
Figure 50. Calculated Currents in the vicinity of Coconut Point with Tidal Stage (insert). ......... 83
Figure 51. Coconut Point pre-construction morphologic evolution (1994 - 1999). ..................... 84
Figure 52. Coconut Point Pre and Post Development Comparison (1999 - 2005). ...................... 85
Figure 53. Calculated Net Sediment Transport Vectors. .............................................................. 86
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Figure 54. Calculated Morphology Change Plot: Existing Conditions ........................................ 87
Figure 55. Terminal Groin Alternative. ........................................................................................ 89
Figure 56. Terminal Groin and Updrift Submerged Structure Alternative ................................... 90
Figure 57. Updrift Submerged Structure Alternative ................................................................... 91
Figure 58. Updrift Emergent Structure Alternative. ..................................................................... 92
Figure 59. Submerged Breakwater Alternative ............................................................................ 93
Figure 60. Emergent Breakwater Alternative. .............................................................................. 94
Figure 61. Floating Breakwater Alternative ................................................................................. 95
Figure 62. Beach Fill Alternative.................................................................................................. 97
Figure 63. Beach Fill and Updrift Emergent Structure Alternative .............................................. 98
Figure 64. Floating Breakwater with Additional Shoreface and Coarse Beach Fill ..................... 99
Figure 65. Calculated Morphology Change: Terminal Groin Alternative .................................. 100
Figure 66. Calculated Currents: Terminal Groin Alternative ..................................................... 101
Figure 67. Calculated Morphology Change: Terminal Groin + Updrift Submerged Structure
Alternative................................................................................................................................... 102
Figure 68. Calculated Currents: Terminal Groin + USS Alternative.......................................... 102
Figure 69. Calculated Morphology Change: Updrift Submerged Structure ............................... 103
Figure 70. Calculated Currents: Updrift Submerged Structure Alternative ............................... 104
Figure 71. Calculated Morphology Change: Updrift Emergent Structure Alternative ............... 105
Figure 72. Calculated Currents: Updrift Emergent Structure Alternative .................................. 105
Figure 73. Calculated Morphology Change: Submerged Breakwater Alternative. .................... 106
Figure 74. Calculated Currents: Submerged Breakwater Alternative. ....................................... 107
Figure 75. Calculated Morphology Change: Emergent Breakwater Alternative ........................ 107
Figure 76. Calculated Currents: Emergent Breakwater Alternative ........................................... 108
Figure 77. Calculated Morphology Change: Floating Breakwater Alternative .......................... 109
Figure 78. Calculated Currents: Floating Breakwater Alternative ............................................. 109
Figure 79. Floating Breakwater Wave Height Comparison. ....................................................... 110
Figure 80. Calculated Morphology Change: Beach Fill Alternative (1 mm) ............................. 111
Figure 81. Calculated Morphology Change: Coarse Beach Fill Alternative (4 mm) ................. 111
Figure 82. Calculated Morphology Change: Floating Breakwater with Additional Shoreface and
Coarse Beach Fill Alternative ..................................................................................................... 112
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Figure 83. Calculated Currents: Floating Breakwater with Additional Shoreface and Coarse
Beach Fill Alternative ................................................................................................................. 113
Figure 84. The file Geodatabase organization in the ArcGIS® interface. .................................. 116
Figure 85. The morphological features presentation in the ArcMap® v 10.2.2. ........................ 116
Figure 86. The Spatial Analyst Tool box and 3D analyst Tools in the Arc Toolbox. ................ 117
Figure 87. Creating flood shoal surface using Kriging tool........................................................ 118
Figure 88. Creating Surface Contour from survey point files: Use of 3D analysts tool. ............ 119
Figure 89. Volume change analysis using cut & fill tool. .......................................................... 120
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List of Tables
Table 1. Summary of Hydrographic Surveys (Source: Sebastian Inlet Tax District). .................... 3
Table 2. Annualized placement and removal volumes for sand budget calculations. .................. 24
Table 3. Annualized volume changes per cell and flux (2005 – 2014). ....................................... 25
Table 4. Annualized volume changes per cell and flux (2009 – 2014). ....................................... 25
Table 5. Annualized volume changes per cell and flux 2012 – 2014. .......................................... 27
Table 6. Aerial Surveys (2004 – 2014). ........................................................................................ 29
Table 7. Temporal domain of shoreline analysis from aerial imagery. ........................................ 30
Table 8. Average rate of change for EPR and LR methods (ft /yr). ............................................. 32
Table 9. Summary of long-term changes for the recent period (1958-2014). .............................. 33
Table 10. Summary of shoreline change rates for the period (2004-2014). ................................. 35
Table 11. Summary of short-term changes for the recent period (2009-2014). ........................... 37
Table 12. Summary of short-term changes for the recent period (2013-2014). ........................... 39
Table 13. Summary of results (including mean shoreline position) from the EPR and LR methods
for aerial data sources. North to South, North and South only extents. ........................................ 64
Table 14. Summary of results (including mean shoreline position) from the EPR and LR
methods for aerial data sources. Sub-cells north extents. ............................................................. 64
Table 15. Summary of results (including mean shoreline position) from the EPR and LR
methods for aerial data sources. Sub-cells south extents. ............................................................. 65
Table 16. Model alternatives summary. ........................................................................................ 88
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1.0 Introduction and Previous Work
This report extends the analysis of the Sate of Sebastian Inlet from the publication of the
2013 report through the summer months of 2014. In the original 2007 report, sand volume
changes, sand budget, and morphological changes between 1989 and 2007 were examined
(Zarillo et al. 2007). In addition, shoreline changes were documented between 1958 and 2007
using aerial images and between 1990 and 2007 using field survey data. In the 2013 report, much
of the long-term analysis presented in the 2007 report was summarized in the main body of the
text and re-stated in a series of appendices. This effort was to present a long term analysis of
inlet evolution and associates management strategies that have been applied over the years.
In the present report, the morphological analysis, sand budget analysis and the shoreline
analysis are updated to 2014. In addition, a model based analysis of Coconut Point on the south
side of the interior of Sebastian Inlet presents potential solutions to the ongoing erosion issues.
Another section of this report describes the effort to consolidate all long term physical and
morphological data sets collected by the Sebastian Inlet District into a comprehensive and well
organized GIS project. Recommendations are made for applying the results of State of the Inlet
Analysis to the ongoing Sebastian Inlet Management Plan.
2.0 Sand Volume Analysis Methods
Hydrographic surveys of the inlet system and surrounding beaches are conducted
annually by Sebastian Inlet Tax District (SITD) since the summer of 1989 (Table 1 lists the
surveys completed in the past decade. Starting in winter 1991, surveys have been performed on a
semiannual basis. Offshore elevation data are gathered by conventional boat/fathometer
surveying methods from -4 ft to -40 ft in accordance with the Engineering Manual for
Hydrographic Surveys (USACE, 1994). Figure 1 shows the study area includes not only the
entire inlet system (ebb shoal, throat, sand trap and flood shoal), but the adjacent beaches as well.
The study area spans approximately 30,000 ft north (Brevard county) and 30,000 ft south (Indian
River County) of the inlet with beach profiles taken about every 500 ft. Such a comprehensive
dataset provides excellent support for volumetric calculations of inlet shoal and morphologic
features, as well as for the analysis of changes in shoreline position through a “zero contour”
extraction technique. This data source is also valuable for calibrating models and other decision
making tools. Additional datasets used for this report update include surveys performed in
2
summer 2013, winter 2014, and summer 2014. The spatial resolution is much greater due to the
use of multibeam sonar in the south region.
Figure 1. Extent of hydrographic survey (2014 summer).
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Table 1. Summary of Hydrographic Surveys (Source: Sebastian Inlet Tax District).
Survey Date Ebb
shoal Channel
Sand
trap
Flood
shoal
North
beach
(ft)
South
beach
(ft)
Jan-04
Jul-04 x x x x 30,000 30,000
Jan-05 x x x 30,000 30,000
Jul-05 x x x 30,000 30,000
Jan-06 x x x x 30,000 30,000
Jul-06 x x x x 30,000 30,000
Jan-07 x x x x 30,000 30,000
Jul-07 x x x x 30,000 30,000
Jan-08 x x 30,000 30,000
Jul-08 x x x x 30,000 30,000
Jan-09 x x x x 30,000 30,000
Jul-09 *5 x x x x 30,000 30,000
Jan-10 *5 x x x x 30,000 30,000
Jul-10 *5 x x x x 30,000 30,000
Jan-11 *5 x x x x 30,000 30,000
Jul-11 *5 x x x x 30,000 30,000
Jan-12 *5 x x x x 30,000 30,000
Jul-12 *5 x x x x 30,000 30,000
Remarks:
1. Poor coverage, no jetty fillet of north beach
2. Poor coverage of north beach, transects every 3000 ft
3. missing section of lower shoreface between R-1 and R-4
4. Poor coverage of flood shoal
5. Multibeam data
4
3.0 Sand Volume Analysis Results
Results presented in the volumetric analysis are divided into two subsections. Section 3.1
presents the volumetric evolution of the sand reservoirs or features in the inlet system (Figure 2)
with plots of net seasonal and cumulative volume change over time. Section 3.2 presents the
volumetric evolution of the inlet littoral cells (masks) used for the sand budget computation
(Figure 3). The calculated net seasonal volume changes (ΔV) serve as inputs to the sand fluxes
(ΔQ) for the budget calculations.
Figure 2. Morphologic features forming the inlet system reservoir.
Channel
North filletSouth filletThroatBypass barAttachment bar
FloodshoalSouth beach bypassbarNorth upper filletOuterpartebbshoal.shp
2000 0 2000 4000 Meters
N
5
Figure 3. Sand budget cells. Note the inlet cell does include the flood shoal.
3.1 Individual Inlet Reservoirs
The volumetric evolution of the ebb shoal (bypass bar) illustrated in Figure 4, shows
volume gains since summer 2012 to summer 2014. Cumulative volume changes during this
period reached approximately +40,000 cubic yards since 2004. The volumetric evolution of the
outer ebb shoal (Figure 5) shows similar volume increase over this 2-year period of about 50,000
cu. The cumulative volume change over the lower ebb shoal since 2003 is about 200,000 cu. yd.
compared to about 75,000 cubic yards for the upper ebb shoal (bypass bar). Recent gains on the
lower ebb shoal could be related to backpassing of the finer fractions of the sand placed on the
beach from dredging of the sand trap in 2012 and 2014.
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Figure 4. Volumetric evolution of the ebb shoal from summer 2004 to summer 2014.
Figure 5. Volumetric evolution of the outer ebb shoal from summer 2004 to summer 2012.
7
The volumetric evolution of the attachment bar are small due to its role as a sediment
redistribution zone (Zarillo et al., 1997). Recent spikes in volume (Figure 6) are most likely
related to handling of beach fill material placed from the 2012 and 2014 sand trap projects. A
similar spike in volume occurred in 2007 when the sand trap was dredged and fill placed on the
beach near the attachment bar.
Net seasonal volume changes for the south jetty fillet reservoir (Figure 7) shows a pattern
of gains associated with the time frame of sand bypass from the sand trap. Most recently a gain
of 10,000 cubic yards occurred as the 2014 bypass project was completed in the spring of 2014.
As illustrated in Figure 7, short term and longer term volume changes are well within 30,000
cubic yards over the past 10 years.
The beach section located immediately north of the attachment bar, including the area
from the south jetty to R2 (Figure 8) generally maintains a low sediment volume and small
volume fluctuations since is somewhat sediment starved. However, volume exchanges occur in
this reservoir near the time of sand trap bypass projects. Some sand backpassing is likely to
cause temporary gains along with subsequent release of this sand, possibly to the lower ebb
shoal. A gain of about 40,000 cubic yards between July, 2012 and subsequence loss of this
volume by January, 2013 could be related to sand moving back to the inlet from the fill placed in
the winter of 2012. Some of this material is likely to have moved to the lower ebb shoal which
gained in volume during this period.
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Figure 6. Volumetric evolution of the attachment bar from summer 2004 to summer 2012.
Figure 7. Volumetric evolution of the south fillet from summer 2004 to summer 2014.
-30000
-10000
10000
30000
Jul-0
4
Jan-0
5
Jul-0
5
Jan-0
6
Jul-0
6
Jan-0
7
Jul-0
7
Jan-0
8
Jul-0
8
Jan-0
9
Jul-0
9
Jan-1
0
Jul-1
0
Jan-1
1
Jul-1
1
Jan-1
2
Jul-1
2
Jan-1
3
Jul-1
3
Jan-1
4
Jul-1
4V
olu
me c
han
ge (
yd
³ )
Volumetric evolution of the Attachment bar
Net seasonal
Cumulative
9
Figure 8. Volumetric evolution of the south beach from summer 2004 to summer 2012.
The volumetric evolution of the reservoirs located in the vicinity of the north jetty (north
upper fillet and north jetty fillet) is presented in Figure 9 and Figure 10, respectively. The
volumetric evolution of the north jetty fillet shows small net gains over the past 10 years.
However, episodic positive and negative sand volume spikes occur as sand arrives from the net
southerly littoral drift and sand is either bypassed to the ebb shoal and around the inlet or
possibly finer fractions are swept into the inlet interior. As shown by the dotted line, the
cumulative volume change approximated is less than about 5,000 cubic yards over the past 10
years.
As shown in Figure 10, the upper north fillet has experienced small net sand volume
change from 2004 to 2014. However, episodic gains and losses of sand volume of up to 100,000
cubic yards occur as littoral drift and storms add or remove sand from the relatively large
reservoir. Short term gains and losses of sand in this fillet have been in the range of 50,000 to
100,000 cubic yards since July, 2012.
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Figure 9. Volumetric evolution of the north jetty fillet from summer 2004 to summer 2014.
Figure 10. Volumetric evolution of the upper north fillet from summer 2004 to summer 2014.
The volumetric evolution of the sand trap is presented in Figure 11. The record from
January, 2012 to July, 2014 clearly marks the recent dredging projects to bypass material and
expand the sand trap in 2014. The figure also illustrates the mechanical bypassing of spring 2012
with the removal of approximately 85,000 cubic yards of sand from the sand trap. In the winter
to spring of 2014, approximately 160,000 cubic yards of material were removed. About 120,000
cubic yards of this material was placed to the south of Sebastian Inlet between R4 and R10.
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Volumetric changes for the flood shoal (Figure 12) showed losses from summer 2011 to
summer 2014. Temporary loss of sand volume from the flood shoal is usually associated with
sand trap dredging, losses during this period were also related to loss of sea grass beds normally
present over the flood shoal surface. Recovery of flood shoal sand volume is expected to occur
as the sand trap fills and sea grass beds recover.
Figure 11. Volumetric evolution of the sand trap from summer 2004 to summer 2014.
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Figure 12. Volumetric evolution of the flood shoal from summer 2004 to summer 2014.
Overall, volume changes of all reservoirs were well within the range of previous
estimates (Zarillo et al., 2013). It must be noted that the sand reservoirs in the inlet vicinity
(north and south jetty filets, south beach, and attachment bar) experienced cumulative changes
over the past 8 years close to 0, suggesting that even though they experienced large seasonal
changes, they remained in dynamic equilibrium. The volumetric changes of the reservoirs
located in the inlet back-bay (sand trap and flood shoal) were most impacted by the spring 2012
and 2014 mechanical bypassing project and sand trap expansion, with large losses for both sand
trap and flood shoal. Sand trap dredging tends to decrease the amount of sand that reaches the
flood shoal via tidal current transport therefore increasing volumetric losses. The large seasonal
fluctuations in the sedimentation were further highlighted in the bathymetric change analysis
section.
3.2 Sand Budget Cells
The sediment budget calculations discussed in the report depend on the analysis of
individual sand budget cells. Consistent with earlier versions of the report (Zarillo et. al. 2007,
2013), five computational masks were created to define the sand budget cells (Figure 3). The
inlet cell encompassing the nearshore zone from R215 in Brevard County to R4 in Indian River
County included the ebb and flood shoals and all other reservoirs discussed in the previous
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section. Annualized volume changes (∆V) for each cell, calculated over different time periods,
were added to the sand budget equation to calculate the littoral sand transport in and out of each
reservoir/cell. Annualized placement and removal volume data were also included to account for
dredging/mechanical bypassing and beach fill activities in the cells concerned. This is presented
in Table 2 in the sand budget section (Section 6.0). Time series of volumetric change for the five
littoral cells (masks) since 2004 are presented in Figure 13 through Figure 17, ranging from the
northernmost to the southernmost distal cells.
Volume changes for the N2 cell, the section between R189 and R203, are presented in
Figure 13. Results indicate small net change in volume over the past decade. This is punctuated
by a volume loss of about 400,000 cubic yards from January to July, 2013 followed by recovery
of more than 300,000 cubic yards from July, 2013 to July, 2014. As indicated by the dotted line,
cumulative change for the N2 cell approximated 100,000 cubic yards since 2004.
Volume changes for the N1 cell, the section between R203 and R215, are presented in
Figure 14. Similar to the N2 cell, volume changes in N2 are usually seasonal; characterized by
gains in the winter months and volume losses in the summer months. This cycle is related to the
stronger south directed littoral drift under winter conditions sending more sand into the N2 and
N1 cells from the beach and shoreface to the north in Brevard County. Littoral drift reversals in
the spring and summer months reversing the direction of transport sends more sand to the north,
which is not replenished by sand bypassing around Sebastian inlet due to the milder wave
regime. Net sand volume change in the N1 cell since 2004 is a loss of nearly 400,000 cubic
yards.
Overall, the magnitude of recent seasonal changes for both N2 and N1 cells was well
within the magnitude observed during the past 10 years. Both cells shared similar volume change
trends, and volume changes have been in phase since 2007.
14
Figure 13. Recent volumetric evolution of the N2 sand budget cell.
Figure 14. Recent volumetric evolution of the N1 sand budget cell.
Volume changes for the inlet cell sand budget cell are presented in Figure 15. Sand
volume in this budget cell is the combination of the flood and ebb shoals, along with sand stored
in the channel and the fillet areas within about 4,000 ft of beach and shoreface to the north and
south of the inlet entrance. Volume fluctuates seasonally showing moderate gains in the higher
energy winter months and moderate losses in the lower energy summer months. Divergence
15
from this pattern can occur in association to major storms or in response to adjustment after a
sand bypassing project from the sand trap. Over the last decade, a net gain of approximately
300,000 cubic yards has been observed. About two thirds of this volume can be attributed by
gains on the outer (lower) ebb shoal as seen in Figure 5. The process involved may be back
passing of sand from fill projects immediately south of Sebastian Inlet. Recent volume gains in
late 2013 and again in the first half of 2014 may be related to removal, placement, and
backpassing of material from the sand trap.
Figure 15. Recent volumetric evolution of the Inlet sand budget cell.
The volumetric evolution of the S1 cell, situated directly south of the inlet cell between
R4 and R16, is presented in Figure 16. The normal volume change pattern in this cell is a
seasonal variation marked by volume gain in the winter and volume loss in the summer as seen
between July, 2007 and July, 2010. The signature of the late 2007 and early 2008 placement of
more than 200,000 cubic yards of sand in this cell is seen in Figure 16. More recently, the
signature of the 2013 and 2014 fill projects from the Sebastian inlet sand trap is apparent. After
the 2007 fill project constructed by Indian River County, the seasonal variations in sand volume
were amplified and followed by slightly declining volumes until 2010. Since 2010, the pattern
has been a decline in sand volume punctuated by volume gains related to sand trap bypass
project. The overall net sand volume change in the S2 cell is near zero for the decade of 2004 to
2014.
16
Figure 16. Recent volumetric evolution of the S1 sand budget cell.
The volumetric evolution of the S2 cell, located between R16 and R30, is presented in
Figure 17. The record of sand volume changes in the cell is one of abrupt gains followed by a
trend of declining sand volume that can extend over several years. The sand budget in the S2
cell is influenced by both the seasonal wave climate, and natural and mechanical bypassing of
sand around Sebastian Inlet. The episodes of strong seasonal gains of sand volume in S2 (Figure
17) are most likely to be due to sand bypassing around the inlet and sand placement updraft of S2
in the S1 cell. A lag time of sand volume increase is required for the sand to reach S2.
Depending on variations in wave climate and storm activity is may take up to a year for sand to
reach this zone from sand bypassing and updrift placement. Net sand volume loss in S2 from
2004 to 2014 is less than 100,000 cubic yards.
17
Figure 17. Recent volumetric evolution of the S2 sand budget cell.
4.0 Bathymetric and Morphologic Change
4.1 Methods
The analysis uses the same dataset and overall methodology as the sand volume analysis
described in the section above. The bathymetric changes section is subdivided according to the
time period of analysis. The time covered in this report is from winter 2013 through summer 2014,
a period of about 18 months. The net bathymetric changes over a 15-year and 20-year periods are
presented in the series of earlier report (Zarillo et al, 2007, 2012, 2013). In the color code for
figures depicting topographic change, blue represents erosion, whereas red indicates deposition.
Topographic changes were combined with results from shoreline changes and sand budget
calculations for a better understanding of the sedimentation processes.
4.2 Seasonal Changes: 2013-2014
Figure 18 shows topographic changes within and adjacent to Sebastian Inlet between the
summer 2013 survey and winter 2014 survey. Among the major features seen in the figure is a
pervasive increase in sediment accumulation on the north side of Sebastian inlet reaching to the
offshore limit of the survey in about 12 meters of depth. This is consistent with the increase in
sand volume seen in the N2 sand budget cell (Figure 13) and particularly in the N1 cell (Figure
18
14) where more than 700,000 cubic yards of sand accumulated during this period. To the south of
Sebastian Inlet, sand accumulation occurred in the S1 and S2 sand budget cells. The largest
accumulation was in the S2 cell.
Figure 19 shows the details of topographic change from summer 2013 the winter 2014
survey near the inlet. Sand deposition generally occurs in the fillet areas (also see Figure 7 and
Figure 9 ). The flood shoal shows patchy changes in topography dominated by erosion (see Figure
12). Sand deposition can be seen over the lower ebb shoal along with some erosions over the crest
of the bypass bar (upper ebb shoal) and slight loss of sand over the attachment bar (also see Figure
6).
Figure 18. Net topographic changes from summer 2013 to winter 2014.
19
Figure 19. Details of net topographic changes from summer 2013 to winter 2014.
The most prominent topographic change in the winter 2014 to summer 2014 survey
intervals is completion of the Sebastian Inlet sand trap expansion and is shown in Figure 20. The
dredging of the sand trap shows as a deep blue pattern in the area between the flood shoal and
west end of the inlet channel. Deposition from the beach to the base of the shoreface to the north
of Sebastian Inlet decreased and in the N1 cell (Figure 3) erosion occurred (also see Figure 14).
The fillet areas to the north and south of the inlet jetties accumulated sand (Figure 21). Both the
flood shoal and lower ebb shoal were depositional during this period. The attachment bar also
accumulated sand during this period as shown in Figure 21 and in Figure 6.
20
Figure 20. Net topographic changes from winter 2014 to summer 2014.
Figure 22 shows topographic changes over the 12 month period between summer 2013 and
summer 2014 while Figure 23 provides a more detailed view of the region closest to the inlet.
This time period includes seasonal changes and the topographic features related to dredging of
the Sebastian Inlet sand trap and placement of sediments on the south side of the inlet between
R4 and R10. The continuous line of positive topographic change as seen in Figure 23 marks the
fill, whereas the deep blue color marks the sand trap expansion. The yellow color pattern on the
lower shoreface indicates sand deposition on the north side of the inlet in the first half of the 12
month period followed by deposition on the south side of the inlet in the final 6-month period.
The lag between deposition on the north and south beaches indicates sand bypassing across the
inlet during the 12 months from summer 2013 to summer 2014. Deposition over the ebb shoal
during this period is likely to be linked to the sand bypassing process, as well as some sand
backpassing from the sand trap based fill project on the south side of Sebastian Inlet.
21
Figure 21. Details of net topographic changes from winter 2014 to summer 2014.
Figure 22. Net topographic changes from summer 2013 to summer 2014.
22
Figure 23. Details of net topographic changes from summer 2013 to summer 2014.
5.0 Sand Budget Update 2012: Methods
A sediment budget uses the conservation of mass to quantify sediment sources, sinks, and
pathways in a littoral cell environment. It is used to quantify the effects of a changing sediment
supply on the coastal system and to understand the large-scale morphological responses of the
coastal system. The sediment budget equation is expressed as:
Equation 1
The sources (Qsource) and sinks (Qsink) in the sediment budget together with net volume
change within the cell (ΔV) and the amounts of material placed in (P) and removed from (R) the
cell are calculated to determine the residual volume. For a completely balanced cell the residual
would equal zero (Rosati and Kraus, 1999). Figure 24 schematically shows how calculations are
made within each cell of the sediment budget model.
residualRPVQQksource
sin
23
Figure 24. Schematics of a littoral sediment budget analysis (from Rosati and Kraus, 1999).
Determination of net volume change for the local sediment budgets for Sebastian Inlet
was based on volumetric analysis masks presented in section 3.0. The sediment budget
encompasses the area between monuments R189 in Brevard County to monument R30 in Indian
River County. Since variability of the seasonal signal overshoots the average range of values in
the sediment budget, the temporal scale of the calculations is based on several time periods
ranging from two to ten years from summer 2004 to summer 2014. The computation cells
(masks) that were used to establish the local sediment budget are schematically shown in the
volumetric section (see Figure 3). Volume changes for each mask were determined according to
the methods described above in the net topographic changes section and input into the Sediment
Budget Analysis System (S.B.A.S) program, provided by the Coastal Inlet Research Program.
Details of these procedures can be found in the technical report by Rosati et al. 2001. Based on
the longshore transport estimates from the Coastal Tech study (1988) and other estimates, an
input value (Qsource) of 100,000 yd3/yr was chosen. The placement values (P) into the S1 (R4 to
R16) and S2 cells (R16 to R30) correspond to the beach fill projects and were included in the
calculations. Removal of sand (R) through mechanical bypassing was included (R) to account for
the spring 2007, 2012, and the 2014 dredging projects within the sand trap. However, removal of
sand (R) through offshore losses was assumed to be zero for all cells, as the boundaries of the
masks extend beyond the depth of closure. Placement and removal values are annualized and
presented in Table 2.
24
Table 2. Annualized placement and removal volumes for sand budget calculations.
Time Period Season
Placement S1
(cy/yr.)
Placement S2
(cy/yr.)
Removal Inlet
(cy/yr.)
2005 - 2014 Winter 39,284 19,289 40,838
Summer 39,284 19,289 40,838
2009 - 2014 Winter 53,571 34,721 56,507
Summer 53,571 34,721 56,508
2012 - 2014 Winter 133,928 42,959 141,269
Summer 72,928 0 80,270
5.1 Sand Budget Results
The sand budget is presented on four distinct time scales ranging from a longer term
budget for the past 15 year and 10-year periods to a short term budget that examines volume
changes and sand flux over single year periods. The budget uses calculated annualized volume
change per cell as inputs. Annualized beach fill material is accounted for in the S1 and S2 cells
(R4-R16 and R16-R30, respectively), along with dredging of the sand trap in 2007, 2012, and
2014.
Interpretation of the fluxes, especially those leaving the southernmost cell (S2, R16-R30)
must consider that the sand budget assumes a fixed input of +150,000 cy/yd. entering the first
north cell (N2). Sand transport was assumed to flow north to south. Positive numbers indicate an
increased flux toward the south, which was likely representative of the Sebastian Inlet area on a
larger scale, whereas negative results indicate a reversal of sediment transport to the next cell
north. Thus a negative volume change for a cell meant that volume was gained in a south cell or
was available for that cell.
A long-term sand budget is listed in Table 3 and covers the period from 2005 through
2014. A comparison is made between winter and summer-based budgets. The annualized sand
budget shown in Table 3 includes net sand volume loss in the N2 and N1 budget cells for this
time period (see Figure 13, Figure 14). This resulted in large values for Q (littoral transport) past
these cells for both the winter and summer sand budgets. In the winter sand budget the inlet cell
25
(see Figure 15 ) retained annual average of about 8,000 cu. yd. of sand, whereas in the summer
sand budget retained an annual average of about 21,000 cu. yd. of sand was retained. The 2005
to 2014 analysis accounts for dredging of the sand trap and fill placement in this period. The
annualized values of fill (placement) and dredging (removal) are listed in Table 2. Thus, in both
the winter and summer sand budgets Sebastian Inlet retains a relatively small amount of sand on
an annual basis and naturally bypasses an annual average of more than 120,000 cu. yd.
Table 3. Annualized volume changes per cell and flux (2005 – 2014).
Time Period Winter 2005 - Winter 2014 Summer 2005 - Summer 2014
Sediment Budget
Cell ∆V (cy/yr) Q (cy/yr) ∆V (cy/yr) Q (cy/yr)
North 2 -12,822 162,822 -10,005 160,005
North 1 -18,027 180,850 -24,135 184,139
Inlet 8,007 132,005 21,184 122,118
South 1 -38,774 210,063 13,876 147,526
South 2 7,218 222,135 10,803 156,013
Table 4. Annualized volume changes per cell and flux (2009 – 2014).
Time Period Winter 2009 - Winter 2014 Summer 2009 - Summer 2014
Sediment Budget
Cell ∆V (cy/yr) Q (cy/yr) ∆V (cy/yr) Q (cy/yr)
North 2 -21,820 171,820 19,267 130,733
North 1 -14,639 186,459 -44,656 175,390
Inlet -18,389 148,341 13,019 105,863
South 1 -78,976 280,888 3,361 156,074
South 2 -43,851 359,460 -80,842 271,637
26
Short-term Sand Budget
The annualized changes and associated fluxes for short-term periods are presented in
Table 5. In the winter 2012 to winter 2014 sand budget, the removal of material from the sand
trap in early 2012 and again in winter 2014 is included in the calculation. Likewise, annualized
placement of fill in the S1 and S2 cells is considered for this period. The summer 2012 to
summer 2014 sand budget considers dredging of the sand trap during the winter of 2014 and the
annualized placement of sand in the S1 budget cell (see Table 1)
In the winter to winter sand budget, deposition in the N2 and N1 cells reduced the initial
flux of sand into N2 the (150,000 cu. yd.) to about 46,000 cubic yard passing though the N2 cell.
Within the inlet cell, the ∆V and Q terms reflect removal of sand from the sand trap and distorts
the sand bypass value to appear as if the inlet is moving sand to the north. However, given the
annualized accumulation of sand in the N1 and N2 cells for this period, it is possible that some of
the fill from the sand trap that was placed on the south beach was back passed to the inlet and
moved to the north. Sand volume losses in the S1 and S2 cells may have been reduced by sand
placement and contributed to the net southward flow of littoral drift through these cells.
The summer 2012 to summer 2014 sand budget calculation was substantially different
from the winter to winter budget. This summer sand budget has less material dredged and placed
and more sand volume added to S1 and S2 cells. The N2 cell retained a similar annualized sand
volume amount compared to the winter budget, whereas the N1 cell lost about 22,000 cubic
yards of sand, which was added to the Q value of transport passing through this cell. The inlet
cell as a whole retained about 69,000 cubic yards on an annualized basis during this period. The
Q littoral transport values are negative from the inlet cell and to the south indicating net transport
from south to north over the 2-year summer to summer time period in a reversal zone to the
south of the inlet. On the other hand the Q littoral transport values north of Sebastian Inlet are
strongly positive driven by the initial input values of 150,000 cubic yards into N1 and erosion in
the N1 cell. The overall summer to summer budget indicated possible conversion of sand from
the littoral system, thus explaining in part retention of sand within the inlet budget cell. Since
previous work indicated that there is strong seasonal variability in the local sand budget and
some variability year to year, caution should be taken when applying short term sand budgets for
27
longer term management of sand resource. Longer term sediment budgets on a time scale of 5
years and longer have proven to be more stable and more useful for long term planning.
Table 5. Annualized volume changes per cell and flux 2012 – 2014.
Time period Winter 2012 - Winter 2014 Summer 2012 - Summer 2014
Sediment Budget
Cell ∆V (cy/yr) Q (cy/yr) ∆V (cy/yr) Q (cy/yr)
North 2 35,856 114,144 34,130 115,870
North 1 67,755 46,389 -22,078 137,949
Inlet 13,897 -108,777 69,133 -11,454
South 1 -16,882 42,105 67,421 -5,945
South 2 -56,642 141,746 48,941 -54,886
28
6.0 Shoreline Changes
Analysis of short term and longer term changes in shoreline position serve as a
compliment to the corresponding analysis of sand volume changes. Although the volume of sand
exchanging between inlet shoals and shoreface reservoirs drives the regional sand budget and
determines the overall dynamic equilibrium of the inlet system, shoreline position service as a
marker of this process that is readily visible. Generally, loss of volume along a segment of beach
and shoreface results in retreat in shoreline position, however, this is not always the case.
Shorelines can occasionally advance even with loss of sand volume on the lower shoreface. This
can be related to onshore movement of sand and steepening of the beach and upper shoreface
slope. In addition, shoreline position can serve as an indication of beachfill performance.
6.1 Methods
Two methods are used to measure shoreline over time in the vicinity of Sebastian Inlet.
One method includes establishing the shoreline position from the semiannual topographic
surveys conducted by the Sebastian Inlet District. The second method is shoreline extraction
from aerial photographs and digital aerial imagery using image analysis techniques. In order to
reach back in time when topographic surveys were not available, aerial photographs were used to
measure shoreline position. The record of high quality aerial photographs extends back to 1958.
From this date until present, control points in the images are recognizable and allow
georeferencing of the images to a horizontal datum.
The details of shoreline extraction methods are provided in the first State of the Inlet
Report completed in 2007 (Zarillo et al, 2007). Methods are briefly summarized here for the
image based analysis. Shoreline positions were digitized from the geo-referenced aerial imagery
for a domain covering approximately 7 miles north to 7 miles south of Sebastian Inlet (~75,000
ft., Table 6). Changes to the shoreline position were determined by comparing 30 time series of
transects generated every 25 ft along the coast. Table 6 of this report lists the aerial image dates
available for the past 10 year (2004-2014). Table 7 indicates the extent of spatial coverage of the
shoreline analysis according to the total number of transects and the alongshore distances.
Transects were generated using the BeachTools© extension for ArcView3.2© from a standardized
baseline (~SR A1A) to the wet/dry line (low-tide terrace). The change in shoreline position was
determined by subtracting the distances along each transect between time-series of interest.
29
Shoreline change rates were calculated using both the End Point Rate (EPR) and Linear
Regression (LR) methods (Crowell et al., 1993; Morton et al., 2002).
Analysis of the shoreline position derived from topographic surveys is based on digitizing
the zero-contour to represent the shoreline. The zero-contour represents the same elevation as the
mean high water line (MHW) for the datum used during the ground survey. Therefore, the
resulting shoreline is considered to be datum-based (Ruggiero et al., 2003). The advantage for
using surveys to determine shoreline position is the improved temporal resolution since
topographic surveys are typically performed on a seasonal basis at Sebastian Inlet. However,
there is a trade-off for spatial resolution since the survey transects are typically spaced 500 to
1,000 ft. apart. The aerial image based shoreline positions on the other hand, are extracted at 25
foot intervals.
Table 6. Aerial Surveys (2004 – 2014).
Fly Dates Scale Quality Coverage (mi.) Source
June, 2014 1:2400 Excellent 7 to 7 SITD
July, 2013 1:2400 Excellent 7 to -7 SITD
July, 2012 1:2400 Excellent 7 to -7 SITD
July, 2011 1:2400 Excellent 7 to -7 SITD
July, 2010 1:2400 Excellent 7 to -7 SITD
July, 2009 1:2400 Excellent 7 to -7 SITD
July, 2008 1:2400 Excellent 7 to -7 SITD
14-Feb-07 — Excellent 6.2 to -6.4 SITD
December, 2005 1:2400 Excellent 7 to -7 BCPA/IRCPA
30
Table 7. Temporal domain of shoreline analysis from aerial imagery.
Domains Transect ID R Marker Miles
North 0-1480 180.5-219 7.0
South 1508-2974 0-37.5 6.9
N3 0-880 160.5-203 4.2
N2 880-1364 203-216 2.3
N1 1364-1480 216-219 0.6
Inlet 1365-1645 BC216-IRC4 1.3
S1 1508-1627 0-3.5 0.6
S2 1627-212- 3.5-16 2.3
S3 2120-2974 16-37.5 4.0
6.2 Shoreline Changes from Aerial Imagery Historical Period (1958-2014)
The results presented and discussed in this section on image-based shoreline change will
focus on the linear regression method. However results obtained through the use of the end-
point-rate (EPR) method are also included (Table 8) despite its use being subject to several
disadvantages. For example, if either shoreline is uncharacteristic, the resulting rate of change
will be misleading; also data between the endpoints that is ignored may produce rates that do not
capture important trends or changes in trends, especially as temporal variation increases (Dolan
et al. 1991). The reader is referred to the 2007 State of the Inlet Report (Zarillo et al, 2007)
version of the report for more information on both the linear regression and end-point-rate
method used. In general, both methods yielded similar results with most of the values in the same
order of magnitude and with either a positive or negative trend in concordance with each other.
The remainder of this section will provide more details on the results obtained for selected
periods.
As compared to 1958, the distance from the baseline to the wet/dry line has advanced by
as much as +34.66 ft. along transects immediately north of the inlet and close to +59.27 ft just
south of the south jetty (Figure 25 and Figure 26) according to the results obtained with the EPR
method. This method also indicates that the average change in shoreline position from 1958 to
2013 is 0.56 ft of advance at an average rate of 0.018 ft/yr (Table 9). In agreement with this
31
trend, the linear regression (LR) method also indicates a long-term trend toward accretion. Close
to seventy percent of the 14 miles of the study area is accreting at an average rate of +0.35 ft/yr.,
while only around twenty-nine percent (29%) of the region shows erosion patterns (Table 9).
32
Table 8. Average rate of change for EPR and LR methods (ft /yr).
Extent Method (’58-’14) (’04-’14) (’09-’14) (’13-’14)
N-S EPR 0.0187 0.1299 1.7272 3.6691
LR 0.3484 -0.3625 1.5876 3.3136
Bre
va
rd C
o.
N EPR 0.5147 -0.6671 2.1342 5.3248
LR 0.6316 -0.8455 1.3626 4.7681
Ind
i
an
Riv
e
r
Co
.
S EPR -0.8159 0.9302 1.3204 2.0367
LR 0.0621 0.1301 1.8138 1.8538
Bre
var
d C
o.
R180.5 –
203
(N3)
EPR -0.0107 -0.0143 1.9936 6.1362
LR 0.4681 0.1426 1.4924 5.0576
R203 –
216
(N2)
EPR 1.1529 -1.2022 2.3354 6.3339
LR 0.8139 -1.8972 1.3111 6.3339
R216 –
219
(N1)
EPR 1.1554 -2.5370 2.1501 -3.9675
LR 1.1041 -3.9436 0.5752 -3.9675
Ind
ian
Riv
er C
o.
R1 – 3.5
(S1)
EPR 1.9757 4.5878 -6.0448 7.8699
LR 2.8050 1.7431 -2.7452 7.8043
R3.5 –
R16
(S2)
EPR -1.2761 -1.1665 1.3445 7.6181
LR
0.7790 -2.8865 0.8305 7.6181
R16 –
37.5
(S3)
EPR -1.3837 1.7641 2.5063 -2.6797
LR
-0.7335 1.6426 3.0125 -2.2684
Inlet
EPR 1.5469 1.4065 -1.5762 2.8643
LR 2.0023 -0.8617 -0.7008 2.8643
33
Figure 25. Change (ft.) in shoreline positions, 1958-2014.
Table 9. Summary of long-term changes for the recent period (1958-2014).
Extent Range (ft /yr) Average LR (ft
/yr) Erosion %
Accretion
%
All Domain -2.01 to +3.69 +0.34 28.94 70.15
North -0.77 to +2.00 +0.63 17.62 82.38
South -2.01 to +3.69 +0.06 40.90 59.03
N3 -0.77 to +2.00 +0.46 29.63 70.37
N2 +0.04 to +1.69 +0.81 0 100
N1 +0.76 to +1.41 +1.10 0 100
Inlet +0.00 to +3.69 +2.00 0 90.39
S1 +0.00 to +3.69 +2.80 0 99.17
S2 -0.04 to +2.61 +0.77 0.61 99.39
S3 -2.01 to +0.81 -0.73 69.82 30.18
-150 -100 -50 0 50 100 150
1841861891901921941961982002022032052072092112132152172192467911131517192122242628303234
Change (ft)
Dis
tan
ce A
lon
gsh
ore
(R
mar
ker
pe
r 1
00
0 f
t)Shoreline Change 1958-2014
dif 1958-2014 2 per. Mov. Avg. (dif 1958-2014)
34
The greatest area of accretion occurs just south of the inlet between the jetty and the
attachment bar (S1) from R2 to R4 with a maximum of +3.69 ft/yr at an average of +2.80 ft/yr.
In contrast, the region from R16 to R 37 (S3) is predominantly erosional with an average rate of
change of -0.73 ft/yr including the maximum erosion rate of -2.09 ft/yr for the entire domain of
the study area (near R-26). The northern sub-domain is also predominantly accreting with only
smaller regions in N3 showing erosional trends near R-185 and R-200 in Brevard County.
6.3 Ten-Year Period (2004-2014)
The trend obtained by analyzing nine time series of data representing the last ten years of
shoreline change indicates the beaches along the 14 miles of shoreline surrounding Sebastian
Inlet are characterized by a mixture of shoreline recession and accretions. Figure 27 shows the
net measured change in shoreline position from 2004 to 2014, whereas Table 10 summarizes
change rates and percentage of the shoreline in either accretion or recession with respect to the
images shoreline.
In this time period both methods (EPR and LR) are in agreement that the majority of the
study area is experiencing erosion. Approximately seventy-six percent (58.5 %) of the entire area
from north to south is erosional with an average rate of change of -0.36 ft/yr (Table 11). The area
immediate to the south jetty down to R-4 includes shoreline advance of about to about 41.29 ft,
whereas the entire north extent has receded to an average of-6.00 ft. at -0.66 ft/yr (Figure 27). A
closer inspection to each sub-domains indicate sub-cells are evenly split between erosional and
accreting. The region immediately south of the inlet from R2-R5 (sub-cell S1) is the only area in
which accretion is occurring at 99% with a rate of change of +1.74 ft/yr.
35
Figure 26. Change (ft.) shoreline positions, 1958-2013.
Table 10. Summary of shoreline change rates for the period (2004-2014).
Extent Range (ft. /yr.) Average LR (ft. /yr.) Erosion % Accretion %
Domain -9.02 to +23.04 -0.36 58.49 40.50
North -7.22 to +23.04 -0.84 80.49 19.31
South -9.02 to +14.37 0.13 37.29 62.64
N3 -4.75 to +23.04 +0.14 75.82 23.84
N2 -5.50 to +1.60 -1.89 84.12 15.88
N1 -7.22 to -2.40 -3.94 100 0
Inlet -7.35 to +4.15 -0.86 41.64 48.75
S1 +0.00 to +4.15 +1.74 0 99.17
S2 -9.02 to +3.32 -2.88 71.86 28.14
S3 -5.55 to +14.37 +1.64 22.57 77.43
-100 -50 0 50 100
1841861891901921941961982002022032052072092112132152172192467911131517192122242628303234
Change (ft)D
ista
nce
Alo
ngs
ho
re (
R m
arke
r p
er
10
00
ft)
Shoreline Change 2004-2014
dif 2004-2014 2 per. Mov. Avg. (dif 2004-2014)
36
6.4 Latest Update (2009-2014)
Analysis of the more recent shoreline changes from 2009 to 2014 indicate the overall
region under study has an average shoreline advance of 8.63 ft. (Figure 27) at a rate of 1.72 ft.
/yr. according to the EPR method (See Table 13), and at a rate of 1.58 ft /yr with the LR method
(Table 11). The accretion trend is encountered throughout the majority of the 14 mile extent
except for slight erosion in sub-cell S1. The overall accretion during this period is in agreement
with the sand budget (see Tables 3 and 4) and included the benefits of sand bypassing from the
Sebastian Inlet sand trap in 2012 and 2014 by the Inlet District and placement of beach fill in
2011 and 2012 by Indian River county.
Figure 27. Change in shoreline position, 2009-2014.
37
Table 11. Summary of short-term changes for the recent period (2009-2014).
Extent Range (ft/yr) Average LR (ft/yr) Erosion % Accretion %
Domain -10.23 to +12.74 +1.58 22.92 66.89
North -4.75 to +6.97 +1.36 18.64 71.30
South -10.23 to +12.74 +1.81 27.68 63.60
N3 -4.75 to +6.96 +1.49 14.30 68.79
N2 -2.32 to +6.97 +1.31 21.44 78.56
N1 -2.68 to +4.96 +0.57 40.17 59.83
Inlet -10.08 to +6.68 -0.70 42.70 47.69
S1 -10.08 to +5.58 -2.74 61.67 37.50
S2 -10.23 to +12.74 +0.83 47.37 52.63
S3 -8.60 to +12.44 +3.01 11.58 73.57
6.5 Latest Update (2013-2014)
Analysis of the most recent shoreline changes from 2013 to 2014 indicate the overall region
under study has an average shoreline advance of 3.66 ft (Figure 28) at a rate of 3.66 ft. /yr.
according to the EPR method (Table 13), and at a rate of 3.31 ft. /yr. with the LR method (Table
12). The accretion trend is encountered throughout the majority of the 14 mile extent except for
erosion in sub-cells N1 and S3. The 2013 to 2014 period includes the benefits of sand by passing
from the Sebastian Inlet sand trap.
38
Figure 28. Change (ft.) in shoreline position, 2008-20134
39
Table 12. Summary of short-term changes for the recent period (2013-2014). Extent Range (ft /yr) Average LR (ft/yr) Erosion % Accretion %
Domain -55.98 to +57.85 +3.31 34.32 55.43
North -31.55 to +35.85 +4.76 26.94 63.00
South -55.98 to +57.85 +1.85 42.33 48.81
N3 -20.51 to +26.22 +5.05 19.98 63.11
N2 -31.55 to +35.85 +6.33 30.72 69.28
N1 -21.84 to +12.87 -3.96 64.10 35.90
Inlet -26.44 to +57.85 +2.86 44.84 45.55
S1 -26.44 to +57.85 +7.80 41.67 57.50
S2 -24.45 to +46.67 +7.61 36.23 63.77
S3 -55.98 to +44.68 -2.26 45.85 39.06
Table 13 provides a summary of the aerial image based shoreline changes by time period,
major section and by subsections or cells. From this table the reader can select longer or shorter
time periods to review total changes and rates of change. Annualized changes can be viewed
according to both end point (EP) calculation and a linear regression (LR) calculation. The
overall pattern of shoreline change is similar to that of the sand budget analysis. Over longer
time periods the rates of change tare smaller, whereas over shorter time periods rates are higher
and more spatially variable
64
Table 13. Summary of results (including mean shoreline position) from the EPR and LR methods
for aerial data sources. North to South, North and South only extents. LR EPR
Spatial
Extent
Temporal
Range
Mean
Shoreline
(ft)
Change Rate
of Mean
Shoreline
(ft/yr)
Change
Rate
(ft/yr)
Mean
Change
(ft)
Mean
Annualized
Change (ft/yr)
Mean
Overall
Change (ft)
Mean
Overall
Change
Rate (ft/yr)
North to
South
1958 to 2014 428.66 0.34 0.34 -0.31 1.59 0.56 0.01
2004 to 2014 437.72 -0.36 -1.01 0.09 -0.84 1.16 0.12
2009 to 2014 430.83 1.58 1.75 1.73 1.73 8.63 1.72
2013 to 2014 429.20 3.31 3.66 3.66 3.66 3.66
North
1958 to 2014 458.99 0.63 0.63 1.32 1.11 15.44 0.51
2004 to 2014 409.34 -0.84 -1.61 -0.64 -1.30 -6.00 -0.66
2009 to 2014 402.95 1.36 1.51 2.13 2.13 10.67 2.13
2013 to 2014 400.86 4.76 5.32 5.32 5.32 5.32
INLET
1958 to 2014 469.72 2.00 2.00 1.66 2.64 46.40 1.54
2004 to 2014 501.70 -0.86 -0.86 1.40 -0.53 12.65 1.40
2009 to 2014 496.48 -0.70 -0.70 -1.57 -1.57 -7.88 -1.57
2013 to 2014 491.31 2.86 2.86 2.86 2.86 2.86
South
1958 to 2014 422.24 0.06 0.06 -0.29 1.28 -24.47 -0.81
2004 to 2014 465.66 0.13 -0.41 0.82 -0.39 8.37 0.93
2009 to 2014 458.28 1.81 1.98 1.32 1.32 6.60 1.32
2013 to 2014 457.16 1.85 2.03 2.03 2.03 2.03
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Table 14. Summary of results (including mean shoreline position) from the EPR and LR methods for aerial data sources. Sub-cells north
extents.
LR EPR
Spatial
Extent
Temporal
Range
Mean
Shoreline
(ft)
Change Rate of
Mean Shoreline
(ft/yr.)
Change
Rate
(ft/yr.)
Mean
Change
(ft)
Mean
Annualized
Change (ft/yr.)
Mean
Overall Change (ft)
Mean Overall
Change Rate (ft/yr.)
N3
1958 to 2014 930.05 0.46 0.47 -1.83 -1.28 -0.32 -0.01
2004 to 2014 347.63 0.14 -1.05 -0.08 -1.04 -0.12 -0.01
2009 to 2014 340.96 1.49 1.80 2.00 2.00 9.96 1.99
2013 to 2014 338.74 5.05 6.13 6.13 6.13 6.13
N2
1958 to 2014 448.97 0.81 0.81 0.68 0.91 34.58 1.15
2004 to 2014 453.68 -1.89 -1.89 -1.20 -1.40 -10.81 -1.20
2009 to 2014 446.32 1.31 1.31 2.33 2.33 11.67 2.33
2013 to 2014 443.66 6.33 6.33 6.33 6.33 6.33
N1
1958 to 2014 617.42 1.10 1.10 1.27 1.34 34.66 1.15
2004 to 2014 623.41 -3.94 -3.94 -2.53 -2.89 -22.83 -2.53
2009 to 2014 610.45 0.57 0.57 2.15 2.15 10.75 2.15
2013 to 2014 612.21 -3.96 -3.96 -3.96 -3.96 -3.96
(A04) (A08) (A11) (A05) (A06) (A09) (A10)
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Table 15. Summary of results (including mean shoreline position) from the EPR and LR methods for aerial data sources. Sub-cells south
extents. LR EPR
Spatial
Extent
Temporal
Range
Mean
Shoreline
(ft.)
Change Rate of
Mean Shoreline
(ft/yr)
Change
Rate (ft/yr)
Mean
Change
(ft)
Mean Annualized
Change (ft/yr)
Mean Overall
Change (ft)
Mean Overall
Change Rate
(ft/yr.)
S1
1958 to 2014 342.33 2.80 2.82 1.97 3.51 59.27 1.97
2004 to 2014 393.67 1.74 1.75 4.58 1.37 41.29 4.58
2009 to 2014 395.33 -2.74 -2.76 -6.04 -6.04 -30.22 -6.04
2013 to 2014 381.77 7.80 7.86 7.86 7.86 7.86
S2
1958 to 2014 374.08 0.77 0.77 -1.67 0.16 -38.28 -1.27
2004 to 2014 402.68 -2.88 -2.88 -1.16 -2.08 -10.49 -1.16
2009 to 2014 392.06 0.83 0.83 1.34 1.34 6.72 1.34
2013 to 2014 390.08 7.61 7.61 7.61 7.61 7.61
S3
1958 to 2014 511.43 -0.73 -0.73 -2.22 2.19 -41.51 -1.38
2004 to 2014 518.23 1.64 0.89 1.60 0.48 15.87 1.76
2009 to 2014 513.40 3.01 3.53 2.51 2.51 12.53 2.50
2013 to 2014 515.04 -2.26 -2.67 -2.67 -2.67 -2.67
(A04) (A08) (A11) (A05) (A06) (A09) (A10)
64
7.0 Survey-Based Shoreline Analysis
7.1 Methods
Analysis of the shoreline position derived from hydrographic surveys was based on
digitizing the zero-contour to represent the shoreline. The zero-contour represents the same
elevation as the mean water line (MHW) for the NGVD 1929 vertical datum used during the
ground surveys. The advantage for using surveys to determine the shoreline position was the
improved temporal resolution since hydrographic surveys are typically performed on a seasonal
basis at Sebastian Inlet. However, there is a trade-off for spatial resolution because transects
were typically spaced 500 ft to 1,000 ft apart. As described in the methods section on analyzing
the evolution of inlet reservoirs, generating a survey-based shoreline began with generating
contour plots using the ImageAnalyst© extension in Arcview3.2©. Once the XYZ data files
from hydrographic surveys were contoured, the extension was also used to highlight the zero-
contour so that this one interval could be digitized to represent the position of the shoreline.
Once highlighted, the zero-contour was extracted by hand-tracing the contour using shoreline-
generating tool in BeachTools© (Hoeke et al. 2001). To determine the change in shoreline
position, a common baseline with a NAD27 projection running along the SRA1A was created
manually using BeachTools©. This extension was also used to generate perpendicular transects
from this baseline to the digitized shoreline every 500 ft, which roughly corresponded to the
interval used in the ground surveys. A total of 120 transects were generated including 60
transects north and 60 transects south of the inlet. For detailed methodology on the shoreline
change calculations, the reader is referred to previous reports (Zarillo et al., 2007, 2009, 2010).
Short Term Seasonal Changes
In this section, survey-based shoreline analysis is presented for the 2013 to 2014 period
to illustrate the magnitude of seasonal variability in shoreline position. Shoreline changes
between summer 2013 and winter 2014 are presented in Figure 29. The north section retreated
from R190 to R219 (-30 to -180 ft.) to the exception of several scattered advancement peaks up
to +70 ft near R192, R200, and R210. The section from R215 to the north jetty (R219)
experienced retreat ranging from -20 to -60 ft. The south section experienced minimal
advancement of +20 ft. near the south jetty (R1) and retreat up to -25 ft from R2 to R3. From R5
to R30, the calculated shoreline changes were larger and characterized by an overall retreat,
65
which peaked near R15 and R30 (-120 and -200 ft, respectively). The plot shows two distinct
erosional waves for this time period.
Figure 29. Survey-based shoreline change from summer 2013 to winter 2014.
Shoreline changes between winter 2014 and summer 2014 (Figure 30) were characterized
by advancement from R190 to R208 (+20 to +120 ft) and retreat near R192, and R199 - R202 (-
20 to -80 ft). The shoreline advanced up to +100 ft near the North jetty (R218 - R219). For the
south beaches, calculated shoreline changes showed advancement from R1 to R8 ranging from
+20 to +50 ft. This was followed by minimal shoreline retreat from R9 - R12 (-30 ft) and
advancement from R13 to R30, with peaks at R20 and R30 (+50 and +120 ft, respectively). It is
important to note that the trends were reversed between the winter and summer analyses time
periods for both the north and south beach sections.
66
Figure 30. Survey-based shoreline change from winter 2014 to summer 2014.
Shoreline changes over the 12-month period between summer 2013 and summer 2014
(Figure 31) showed more variable shoreline positions on the north beaches with advancement
and retreat peaks ranging from -100 to +100 ft. Overall, the peaks seem to balance out between
R190 to R219. The south section was characterized by retreat (-40 ft) from R2 to R4, and
advancement from R3 to R8 (+50 ft). This section in particular benefits from sand placement
removed from the sand trap during the winter of 2014. From R9 to R16, shoreline retreated
significantly with a peak near R14 (-180 ft). From R17 and beyond, shoreline retreat ranged from
-25 ft near R20 to almost -100 ft near R30.
Shoreline changes over the 12-month period between winter 2013 and winter 2014 are
shown in (Figure 32). Shoreline recession was persistent over almost of the shoreline segments
both north and south of Sebastian Inlet. Sand placement to the south of Sebastian Inlet was
completed beginning in February winter of 2014, but most of the placement was completed in
67
the late spring. Thus, there was no clear signature of the fill in the shoreline record from early
winter.
Figure 31. Survey-based shoreline change from summer 2013 to summer 2014.
Figure 32 Survey-based shoreline change from winter 2013 to winter 2014.
68
Long Term Shoreline Changes
Long-term shoreline change was assessed through 5-year and 9-year time periods
between 2005 and 2014. The time periods were designed to match with aerial images dates so
comparisons could be made with image-based shoreline changes. Time periods also matched
with sand budget calculations.
Shoreline changes between summer 2009 and summer 2014 (Figure 33) show
advancement ranging from +40 to +150 ft between R markers R190 and R208, with the
exception of retreat peaks near R192 and R199. Between R208 and R211, the shoreline also
retreated up to -100 ft. The remaining section of north beaches experienced shoreline
advancement between R211 and R216, ranging from +20 to +100 ft, and retreat between R216
and R218. In the vicinity of the north jetty near R219, shoreline advanced up to +80 ft. The south
section experienced retreat ranging from -50 to almost -80 ft between R1 and R2. Between R3
and R12, shoreline advanced from +40 to +90 ft. The remaining section of the south beach
showed shoreline retreat up to -70 ft between R14 and R30, to the exception of advancement
between R19-R21.
Shoreline change over a 9-year period are presented in Figure 34 and considered as the
decadal analysis time frame because of missing survey data for the summer of 2004. Shoreline
change between summer 2005 and summer 2014 were characterized by similar large scale
trends. The main differences for the north beaches included an overall retreat ranging from -50 to
-80 ft between R206 and R219. For the south beaches, the shoreline advanced between R1 and
R7 (+20 to +80 ft) which was followed by retreat between R8 and R16 (-30 to -80 ft), like in the
5-year results. The remaining section experienced advancement which peaked near R17 and R30
(up to 120 and 200 ft, respectively).
69
Figure 33 Survey-based shoreline change from summer 2009 to summer 2014.
Figure 34 Survey-based shoreline change from summer 2005 to summer 2014.
70
The long term shoreline change plots illustrated well the effect of the mechanical
bypassing projects in maintaining a stable/advancing shoreline in the southern section. Both 5-
year and 9-year plots indicated overall advancement on the sections located north and south of
the fill placements areas, from R1 to R10 and R16 to R30. Minimal retreat was observed in the
beach fill zone (R10 to R16) in the 5-year summer plot. The magnitude of the shoreline retreat
was more severe in the 9-year period. The 5-year and 9-year shoreline changes for the winter
period were presented in Figure 35 and Figure 36 . Trends were similar to those calculated for
the summer time periods and reinforce the idea of a stable shoreline south of Sebastian Inlet
resulting from beach fill projects. This was particularly illustrated in the overall shoreline
advancement from R1 to R25 for the 5-year period (Figure 36).
Abnormal peaks (advancement or retreat) such as the one that occurred next to the jetty (-
200 ft) in the 5-year and 9-year winter plot could be explained by the lower spatial resolution in
the survey data. Some of the variability could be explained by seasonal variations, therefore it is
important to consider the results of both summer and winter calculations in the final
interpretation of shoreline changes.
Figure 35 Survey-based shoreline change from summer 2005 to summer 2014.
71
Figure 36 Survey-based shoreline change from summer 2009 to summer 2014
The comparison between survey-based (summer 2014) and aerial-based (July, 2014)
shoreline position is presented for the north and south sections, respectively (Figure 37 and
Figure 38). The pattern of shoreline positions between the two analyses is similar, but results
indicated reversed relative position as compared with previous years. Overall the image
shoreline positioned between +50 ft to +140 ft landward of the survey shoreline. However,
spatial variability exists in the trends and reversals occur in the north domain (R205 and R209),
in which he survey shoreline located landward of the image shoreline. Results from previous
comparisons show the imaged based shorelines usually seaward of the survey based shoreline
Sebastian Inlet work (Zarillo et al., 2011, 2012, 2013). The survey-based shoreline pattern is
spatially more variable compared to image-based shorelines due to much lower spatial resolution
of the raw survey data. The survey lines on which the shoreline is based is measured every 500
to 1000 ft (Figure 39). The raw shoreline data is captured every 100 ft in the aerial images and
later resampled at 500-foot intervals for presentation in this report.
72
Figure 37. Comparison of aerial vs. survey based shoreline position for summer 2013 (North
domain).
Figure 38. Comparison of aerial vs. survey based shoreline position for summer 2013 (South
domain).
189
194
199
204
209
214
219
0 100 200 300 400 500
R -
Mo
nu
men
t (B
rev
ard
co
un
ty)
Distance from baseline (ft)
Aerial image
Survey (0 contour)
0
5
10
15
20
25
30
0 100 200 300 400 500 600 700
R -
Mo
nu
men
t (I
nd
ian
Riv
er
Co
un
ty)
Distance from baseline (ft)
Aerial image
Survey (0 contour)
73
Figure 39. Image-based vs. image-based shoreline comparison.
74
8.0 Hydrodynamic and Morphodynamic Numerical Modeling
8.1 Introduction
The north shoreline of Coconut point has suffered chronic erosion over the past few
years. In order to evaluate potential mitigation for this issues the Sebastian Inlet Coastal
Processes Model was modified to include high resolution computational cells along the interior
of the main inlet conveyance channel. After verifying that the model produced good results for
the existing conditions a series of model tests were conducted to evaluate shore protection
methods
8.2 Coconut Point Site Characterization
Repeated field reconnaissance showed increasing erosion along the boat ramp portions of
Coconut Point located on the north shore. Field investigation was performed in June 2014;
December 2014; and again in January 2015. Various construction materials were exposed during
all reconnaissance visits. Erosion was apparent along the entire length of the construction project
adjacent to the parking area. During the first field reconnaissance on June 14th, 2014, dark, fine
grained material was present on the northern shore of Coconut Point in a thin layer on top of the
hard beach construction materials. Figure 40 shows the fine grained material in the left panel and
the right panel shows the beginning of the construction material exposure. The left panel was
taken near the western end of Coconut Point while the right panel was located towards the
eastern end. The right panel of Figure 40 shows very little dark fine grained material and partial
coverage with lighter colored fine grained sand.
75
Figure 40. Fine Grained Material on Coconut Point (Panel a, left) Facing due East; (Panel b, right)
Fine grained material and exposed concrete blocks on eastern end of construction area.
Figure 41. Exposure of Concrete Blocks and Erosion of Shoreline (Panel a, left) Facing due West;
(Panel b, right) Facing due North East
Figure 41 shows field photos taken in December of 2014 and again in January 2016 on
the northern shore of Coconut Point. These photos were taken approximately 6 and 7 months
after the initial site visit and show the removal of fine grained material. Several additional rows
of concrete block were exposed by December and January. Figure 42 demonstrates the exposure
of the plastic cellular material which is placed adjacent to the concrete blocks. In panel b of
Figure 42, shoreline scarping is observed. A scarp can be defined as “…near-vertical cuts caused
76
by wave action during higher water levels…” (Dean, 2003). This indicates that waves are
reaching the uppermost portion of the profile either during high tide or during storms.
Figure 42. Plastic Cellular Material Exposure (Panel a, left) Field Photo facing due West; (Panel b,
right) Facing due West.
Shoreline erosion was most evident at locations where different materials were placed
adjacent to one another. Figure 43 demonstrates the erosion between different materials. In the
left panel, perspective is facing due south and erosion has continued into the soil. Right panel
77
with perspective downward details the erosion between the plastic cell material and concrete
block material.
Figure 43. Shoreline erosion at interface between concrete block and plastic cell material.
A section of shoreline due east of the area is hardened with rubble mound materials.
During the January field visit, a depression was observed and underlying geotextile was exposed.
Figure 44. Google Earth Aerial Image, (Panel a, left); Rubble Mound Depression (Panel b, right).
78
Figure 45 details the approximate location of exposed construction materials and erosion
condition.
Figure 45. Coconut Point Construction Materials (Google Earth, 2014).
8.3 Model Development
A high resolution coastal processes model was In order to evaluate alternatives to reduce
the erosion issues at of Coconut Point. As described in Zarillo, 2012, the Coastal Modeling
System (CMS) is used for hydrodynamic, wave and morphodynamic numerical modeling. The
CMS is “…an integrated 2D numerical modeling system for simulating waves, current, water
level, sediment transport and morphology change at coastal inlet and entrances” (USACE 2014).
The model is developed and maintained by the Coastal Inlet Research Program (CIRP) at the
United States Army Corps of Engineers – Engineering Research and Development Center
(USACE – ERDC), Coastal and Hydraulics Laboratory (CHL) since 2006. The CMS contains
both Wave and Flow models which are run implicitly inline on desktop computers. Calculations
such as hydrodynamics and waves are passed between the Wave and Flow models in steering
79
intervals. The CMS files including grids, plotting and post processing can be developed using the
Surface Water Modeling System (SMS) developed by Aquaveo. The components and processes
included in the CMS are shown in Figure 46.
Figure 46. CMS components (CIRP, 2014).
A significant study for model Verification and Validation (V&V) of the CMS is
documented in Demirbilek (2011), Lin (2011), Sanchez (2011a) and Sanchez (2011b). Further
documentation of the CMS including processes and numerics are documented in Wu (2010), Lin
(2008), Camenen (2007) and Buttolph (2006).
80
Model refinement was increased around Coconut Point to 5 m by 5 m resolution and
more closely matched post construction configuration using latest available aerial imagery
derived from Google Earth database. Figure 47 shows the refinement and grid configuration
around Coconut Point with aerial imagery in the left panel. Aerial imagery was taken in February
2014. Panel b on the right of Figure 47 shows the grid configuration with the initial bottom
topography contours using the latest available data.
Figure 47. (Panel a, left) Grid refinement around Coconut Point with aerial imagery (panel b, right)
depth contours around Coconut Point (aerial imagery: Google Earth, 2014).
Additional topography was included to better represent the upper shoreface or foreshore
as shown in Figure 48. Land and Sea single beam survey transects are shown with the latest
available USACE Lidar Coverage on Coconut Point. These datasets were merged to provide a
singular topography dataset to map to the flow and wave grid. Several alternatives were also run
with additional shoreline cells to examine the effect of additional model run up.
81
Figure 48. Topography Dataset Coverage.
A constant nearshore refinement grid configuration was used for all model runs due to
previous model performance. Modal grain size sediments were also used for all model runs.
Modal grain sizes were adjusted for some alternative runs and will be detailed in later sections.
Additional rip rap cells and associated roughness were added to the flow and wave grids to more
closely represent the present structural configuration of Coconut Point.
8.4 Hydrodynamic Characterization
In order to understand the processes at Coconut Point to develop a suite of alternatives to
test, the flow patterns around Coconut Point were fully characterized. The model was run with
latest available forcing and increased grid resolution. Calculated flow conditions includes waves
and currents and will be presented in the following section.
Waves
The average calculated wave height is 0.03 m (0.01 ft.) with a maximum of 0.08 m (0.03
ft.) during a typical winter forcing spanning the first half of the calendar year (January through
June). Most of the waves are directed onshore of Coconut Point in a south westerly direction.
82
Waves are wind generated but do interact with the complex geometry of the inlet. The inlet
filters out the longer period waves, which are commonly found on the adjacent ocean shoreline.
Boat wake has not been incorporated into the modeling at the time of this report but do pose an
important forcing mechanism for sediment transport. Figure 49 shows the wave height and
associated wave vectors near Coconut Point. Warmer colors indicate larger wave heights while
cooler colors indicate smaller waves. Wave vectors indicate direction the waves are moving
towards. The wave rose inset denotes wave direction towards for the entire winter run. Wave
information was extracted at 1.5 m water depth near the northern shore of Coconut Point.
Figure 49. Calculated Wave Height and Vectors with Wave Rose inset.
Currents
Figure 50 compares typical flow conditions around Coconut Point during flood and ebb
tide. Deeper blues indicate faster current speeds whereas lighter blues indicate slower current
speeds. Current vectors are also plotted indicating the direction of flow.
83
Figure 50. Calculated Currents in the vicinity of Coconut Point with Tidal Stage (insert).
During flood tide, the flow moves alongshore of Coconut Point and slightly increases
towards the distal end. Ebb flow conditions create larger current speeds around the distal end of
Coconut Point and a complex recirculating pattern nearshore. During portions of the ebb tide,
flow closest to Coconut Point continues in the flood direction and eventually reverses. This
recirculating pattern is most like due to the geometry of Coconut Point to the inlet throat. This
flow pattern supports the observed geomorphology of Coconut Point moving material from the
eastern to west.
Observed Morphologic Evolution of Coconut Point
In order to provide a link between the computational elements of the site characterization
and field data nearest the area of interest, a series of aerial images was obtained via Google Earth
to observe the morphologic evolution of Coconut Point through time. A series of shorelines were
constructed using the wet/dry line as a guide. A series of 18 aerial images was collected from the
Google Earth database to examine the morphological evolution of Coconut Point which spans 20
years from March 1994 to February 2014. If coverage allows, future analysis could extend the
morphological evolution of Coconut Point using the aerial imagery used for shoreline analysis
(Section 7.0).
84
Shorelines are a constantly changing parameter and these shorelines are intended to
provide a qualitative assessment of sediment movement during this time period to support the
computational prediction of morphology change. A more rigorous analysis combining aerial
imagery and available Lidar data could be performed to provide a more quantitative assessment
to determine volume changes through time. However, the availability of Lidar data is limited in
this area. Metadata available is also limited for these images. Additional information on the
aerial images including time of day is not known, making relation to tidal phase not available at
this time. Shorelines were drawn at the image of wet dry line.
The various construction activities have influenced morphology change at Coconut Point.
Only 2 images are presently available before the land mass began development, 1999 and 1994.
The shoreline configuration of March 1994 is super imposed onto the aerial imagery of February
1999 in Figure 51. Over the roughly 5 years, the distal lobe of Coconut Point eroded by
approximately 25 m. The south west orientation of Coconut Point remained relatively constant
during this time.
Figure 51. Coconut Point pre-construction morphologic evolution (1994 - 1999).
85
Examining the behavior over 6 years from 1999 to 2005, material is eroded from the
southern flank of Coconut Point and the northern shoreline accreted northward as shown in
Figure 52. During this time period, several structures were installed including the bath houses. It
is unclear if the shoreline stabilization on the northern shore was constructed prior to 1999.
Figure 52. Coconut Point Pre and Post Development Comparison (1999 - 2005).
Calculated Sediment Transport Pathways and Morphologic Evolution
Material moving from the distal end of Coconut Point is evident in both Figure 51 and Figure 52.
Considering the calculated currents around the land mass, material loss south west ward is most
likely a significant sediment pathway. These pathways are illustrated in Figure 53. The arrows
indicate the direction and magnitude of net sediment transport which closely follows the shape of
the shoal formation at the distal end of Coconut Point.
86
Figure 53. Calculated Net Sediment Transport Vectors.
Figure 54 shows the calculated morphology change plots for winter and summer conditions at
the end of six months. Cooler colors indicate erosion while warmer colors indicate accretion. For
both conditions, a shoal feature is formed at the distal end of Coconut Point. A pattern of erosion
and accretion occurs at the south western end of the area of interest. A distinct area of accretion
located at the southwest tip of Coconut Point corresponds to a sand spit that can often bee seen in
this area (See Figure 52). The erodes are adjacent to the spit shows the location of an existing
channel that is in re4sponse to strong ebbing currents as shown in Figure 50.
87
Figure 54. Calculated Morphology Change Plot: Existing Conditions
8.5 Coconut Point Alternatives
The following section details the various modeling alternatives and the approach.
Design Considerations
The design of each alternative intended to generate a balance between effectiveness and what is
most likely to have a successful permitting process. The hydrodynamic characterization A series
of alternatives were develop to address the erosion occurring at Coconut Point. Alternatives
included structural, non-structural and combination of structural and non-structural approaches.
Any structural alternatives (hard, soft or combination) must adhere to the following criteria;
Reduce erosion of material from Coconut Point either from wave action and/or currents
Minimize disruption of use of Coconut Point including beach access
Minimize navigation disruption through the inlet in the vicinity of the flood shoal.
A summary table of the model alternatives is shown in Table 16.
88
Table 16. Model alternatives summary.
Alternative Description
Terminal Groin
Terminal Groin Shore perpendicular structure located at the distal
end of Coconut Point
Terminal Groin + Updrift Submerged Structure Above with a submerged structure oriented
perpendicular to the shoreline due east of Coconut
Point
Updrift Structure
Updrift Submerged Structure A submerged structure oriented perpendicular to
the shoreline due east of Coconut Point
Updrift Emergent Structure Above but designed above the water line.
Shore Parallel Breakwater
Submerged Breakwater A submerged structure offshore of Coconut Point
oriented parallel to the shoreline
Emergent Breakwater A structure designed above the water line located
offshore of Coconut Point oriented parallel to the
shoreline
Floating Breakwater + Additional Shoreface A rigid moored structure located offshore of
Coconut point oriented parallel to the shoreline
with additional shoreface cells activated
Beach Fill
Beach Fill Medium – Coarse Sand A beach fill constructed with medium to coarse
sand with a median grain size of 1 mm
Beach Fill Coarse Sand A beach fill constructed with coarse sand with a
median grain size of 4 mm
Beach Fill Coarse Sand + Updrift Emergent
Structure
Coarse fill material at median grain size of 4 mm
sand with an updrift emergent structure
Floating Breakwater + Additional Shoreface + 4
mm Beach Fill
Rigid moored shore parallel structure combined
with additional shoreface and coarse beach fill
material
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The following sections discuss the design considerations for each structural component.
Terminal Groin
The terminal groin alternative includes a groin constructed at the distal end of Coconut
Point as shown in Figure 55. A groin is a “…shore-perpendicular structure intended to trap sand
from the littoral system or hold sand placed in conjunction with a beach nourishment project”
(Dean, 2003). Terminal merely indicates the ending groin. These structures “…function best in
areas which there is a strong longshore sediment transport” (Dean, 2003). The groin is
represented in the model by non-computational (land) cells with a crest of 2 m above MSL. The
length of the groin is 63 m (206 ft.) and spans the tidal channel and nearly meets the existing
shoal feature which runs parallel to Coconut Point. It is assumed that a structure of this type
would be constructed as rubble mound which is consistent with other structures in the area.
Figure 55. Terminal Groin Alternative.
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Terminal Groin and Updrift Submerged Structure
This alternative combines the terminal groin with an updrift submerged structure and is
shown in Figure 56. The terminal groin has the same configuration as the previous alternative.
The updrift submerged structure crest has been set at 0.5 m below MSL and expressed in the
model as non-erodible hard bottom cells. The hard bottom cells are represented as red symbols in
Figure 56. Roughness has been increased to match rubble mound material and is also represented
in the wave model grid. The intention behind the submerged structure is to reduce current speeds
of water flow closest to the shoreline of Coconut Point and park lands. Reducing current speeds
encourages the deposition of sediment and reduces the erosional capability of the flowing
currents. The submerged structure could be constructed with either rock or reef balls.
Figure 56. Terminal Groin and Updrift Submerged Structure Alternative
Updrift Submerged Structure
In order to examine the effectiveness of the updrift submerged structure without the
influence of the terminal groin, a model alternative was generated with the updrift submerged
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structure only. The structure has the same configuration as the previous alternative but moved
downdrift (westward). The updrift submerged structure grid configuration is shown in Figure 57
and is represented by red symbols. The crest height of the submerged structure is set at 0.5 m
below MSL.
Figure 57. Updrift Submerged Structure Alternative
Updrift Emergent Structure
The placement of the updrift emergent structure is identical as the updrift submerged structure
but with a crest height of 0.5 m above MSL as shown in Figure 58.
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Figure 58. Updrift Emergent Structure Alternative.
Shore Parallel Breakwater
A series of shore parallel breakwater alternatives have been developed; submerged,
emergent and floating. The primary objectives of a nearshore breakwater system is described in
Chapter 3 of USACE, 2002 and are as follows;
Increase the fill life (longevity) of a break-fill project,
Provide protection to upland areas from storm damage,
Provide a wide beach for recreation, and
Create or stabilize wetland areas.
The breakwater alternatives selected are continuous along the length of Coconut Point.
Additional configurations could be investigated such as shorter breakwaters with gaps. The
design considerations will be described in the following sections.
Submerged Breakwater
The intention of the submerged breakwater is to reduce the wave energy on the lee side of
the structure to reduce material loss and encourage material deposition. For this situation, the
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formation of a tombolo on the lee side of the structure would be advantageous. Figure 59 shows
the grid configuration for the submerged breakwater alternative.
Figure 59. Submerged Breakwater Alternative
The crest of the submerged breakwater is set at 0.5 m below MSL and expressed as hard
bottom cells with adjusted roughness. If constructed, a breakwater would most likely be
constructed with rubble mound material similar to other structures near the study area. The
structure was incorporated into the model grid with a trapezoidal shape. The breakwater is
situated roughly parallel to Coconut Point on top of an existing shoal feature. Total length of the
breakwater alternative is approximately 120 meters which spans nearly the length of the
construction area of Coconut Point focusing on the areas showing the greatest loss of material.
The structure is placed approximately 26 meters from the shoreline to allow flow to continue
between the structure and Coconut Point but also avoid the existing navigation channel. Other
configurations for future study include segmenting the breakwater to increase flushing behind the
structure.
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Emergent Breakwater
The emergent breakwater alternative is identical configuration to the submerged
breakwater with the crest of the structure at 0.5 meters above MSL. Figure 60 shows the grid
configuration of the emergent breakwater alternative.
Figure 60. Emergent Breakwater Alternative.
Floating Breakwater and Additional Shoreface
The floating breakwater is represented in the wave model with a specified draft per cell.
A description of the mathematical implementation of the floating breakwater is detailed in Lin,
2008. The average water depth at the structure location is 1 m and the configuration is presented
in Figure 61. Additional shoreface cells were added to observe the impact of the floating
breakwater on wetting and drying occurring in the foreshore.
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Figure 61. Floating Breakwater Alternative
The floating breakwater is implemented with a 0.4 m draft and is situated on top of an existing
shoal feature. The structure spans nearly the entire length of Coconut Point in an effort to
provide wave sheltering to a majority of Coconut Point while maintaining access for small boats.
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Beach Fill
A beach has been constructed in the model domain to match the slope of the existing
beach as derived from 2007 LIDAR data (FDEM). The additional LIDAR coverage can be
observed in Figure 48. Coarse beach fill material was implemented in the model in concert with
additional foreshore cells to increase the number of cells that would experience wetting and
drying. The foreshore can be described as the swash zone and is “…the region of the profile that
is alternatively wet or dry as the waves rush up this steep portion of the profile” (Dean, 2003).
Beach fill was implemented by adjusting the median grain size dataset (D50) to coarser material.
Two different model runs were performed with beach fill; one with a median grain size of 1 mm
and a second with 4 mm. Both grain sizes are defined as coarse sand using the Wentworth size
class. Figure 62 details the location of the coarse beach fill within the model and is indicated by a
red polygon.
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Figure 62. Beach Fill Alternative
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Beach Fill with Updrift Emergent Structure
A secondary beach fill alternative type was developed combining a coarse beach fill of 4
mm with an emergent updrift structure. This alternative is shown in Figure 63 with the beach fill
planar extents indicated by a red polygon and the updrift emergent structure is shown as red
symbols. 4
Figure 63. Beach Fill and Updrift Emergent Structure Alternative
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Floating Breakwater with Additional Shoreface and Coarse Beach Fill
An alternative combing the floating breakwater and coarse beach fill with additional cells
for wetting and drying was developed and shown in Figure 64. The floating breakwater location
is indicated by a black polygon while the beach fill extents are represented by a red polygon.
Figure 64. Floating Breakwater with Additional Shoreface and Coarse Beach Fill
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Alternative Results
The results of the model alternatives are presented as a series of morphological change
plots with current plots since the primary interest is the predicted response of Coconut Point and
the surrounding areas to construction activity. Additional computed elements such as wave
heights or currents may be used to further elucidate results for a particular alternative. Both
winter and spring climates were run for each alternative and both climates showed similar
morphological results. For brevity, only one climate will be presented in each section.
Terminal Groin
Morphology change plots for the terminal groin alternative are shown in Figure 65. For
comparison, calculated existing conditions are shown in the left panel and the model alternative
in the right panel. Warmer colors indicate accretion while cooler colors indicate erosion.
Figure 65. Calculated Morphology Change: Terminal Groin Alternative
The terminal groin prevents the formation of a shoal at the south western portion of the
shoreline which is visible in the existing conditions. However, the structure does provide
sheltering adjacent to the structure on the eastern bank. Erosion is observed in the existing
conditions run at approximately the midpoint of the northern shore of Coconut Point. The
terminal groin reduces this erosion but also blocks sediment accretion near the shoreline. A shoal
forms on the western bank of the structure. The implementation of the terminal groin may
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deposit additional sediment in the navigation channel that wraps around the distal end of
Coconut point. Figure 66 plots the current magnitude and direction for the terminal groin
alternative. This figure includes flood tide on the left panel and ebb tide on the right panel. The
currents are blocked by the terminal groin during the ebb tide and prevents material from
reaching the south western portion of Coconut Point. Vectors indicate towards the direction of
flow and deeper blues indicate stronger currents while lighter blues indicate currents of lesser
intensity.
Figure 66. Calculated Currents: Terminal Groin Alternative
Terminal Groin + Updrift Submerged Structure
This alternative combined the terminal groin with an updrift submerged structure. Figure
67 shows the calculated morphology change for this alternative with existing conditions in the
left panel and the alternative condition in the right panel. Warmer colors indicate shoaling while
cooler colors indicate erosion. The updrift submerged structure is indicated by green symbols
which represent hard bottom in the model set up. Directly adjacent to the updrift submerged
structure are additional hard bottom cells which are present in every run. This hard bottom
represents the known extents of exposed rock in the inlet throat.
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Figure 67. Calculated Morphology Change: Terminal Groin + Updrift Submerged Structure
Alternative
Whereas the structures reduce the erosion observed onsite during this time period, no accretion
was observed. Figure 68 presents a comparison of flood (left) and ebb (right) flow conditions.
Figure 68. Calculated Currents: Terminal Groin + USS Alternative
A reduction in current magnitude due to the updrift submerged structure was observed. This is
most apparent on the flood tide when looking at the region between the two structures in Figure
68 and then comparing that area to the terminal groin only alternative in Figure 66. The flood
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tide flow conditions is less intense with the updrift submerged structure in place. However, the
complex re-circulatory nature of the flow on the ebb tide was not greatly impacted by the updrift
structure. Since the terminal groin indicated the possibility of increasing channel infilling,
variations including a terminal groin were not investigated further.
Updrift Structures
A pair of alternatives were run using a shore perpendicular structure placed east of
Coconut Point. The intention behind these alternatives is to examine the response of the system
to slowing down the current magnitude
Updrift Submerged Structure
The calculated morphology change for the updrift submerged structure alternative is
shown in Figure 69. Warmer colors indicate accretion while cooler colors indicate erosion. The
structure is represented by green symbols extending outwards perpendicular to the shoreline.
Other green symbols present represent hard bottom specified within the model domain. A small
shoal feature developed over the 6 month simulation period. Less erosion was observed on the
downdrift side of the structure as compared with the existing conditions. This behavior is
reflected in the flow fields presented in Figure 70.
Figure 69. Calculated Morphology Change: Updrift Submerged Structure
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A comparison between the flow conditions during mid flood and ebb tide is shown in Figure 70.
A shadow is observed on the western side of the structure during flood tide indicating that the
current speeds are reducing after flowing over the submerged structure. A smaller shadow is
observed on the eastern side of the structure during ebb tide.
Figure 70. Calculated Currents: Updrift Submerged Structure Alternative
Updrift Emergent Structure
The calculated morphology change of the updrift emergent structure alternative is presented in
Figure 71.
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Figure 71. Calculated Morphology Change: Updrift Emergent Structure Alternative
Figure 72. Calculated Currents: Updrift Emergent Structure Alternative
Shore Parallel Breakwater
The results of the shore parallel breakwater alternatives will be presented in the following
sections. The breakwater types included submerged, emergent and floating.
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Submerged Breakwater
The calculated morphology change for the submerged breakwater alternative is shown in
Figure 73. Warmer colors indicate accretion while cooler colors indicate erosion. The submerged
breakwater is represented by green symbols which are defined as hard bottom. Erosion is
observed on the lee side of the structure which is most likely due to the impact of current speeds
between the structure and the shoreline. A shoal continues to form at the distal end of Coconut
Point and meets the south western end of the breakwater.
Figure 73. Calculated Morphology Change: Submerged Breakwater Alternative.
A comparison of flow conditions between flood and ebb tide is shown in Figure 74. The
flood tide condition is shown in the left panel while the right panel represents the ebb condition.
Some of the recirculation during the ebb portion of the tide is reduced with the inclusion of the
submerged breakwater. During flood tide, a shadow is created on the south western tip of the
breakwater and this reduction in current magnitude is most likely responsible for the shoal
extending from the southwestern tip of the breakwater as seen in Figure 73.
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Figure 74. Calculated Currents: Submerged Breakwater Alternative.
Emergent Breakwater
Figure 75 presents a comparison between calculated existing conditions and the emergent
breakwater alternative for morphology change. Warmer colors indicate accretion while cooler
colors indicate erosion. A shoal feature forms at the south western end of the structure and
extends towards the distal end of Coconut Point. This shoal is similar in configuration to the
submerged breakwater as shown in Figure 73 but may be slightly larger in magnitude.
Figure 75. Calculated Morphology Change: Emergent Breakwater Alternative
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Figure 76 shows a comparison of flow conditions between flood and ebb tide for the
emergent breakwater alternative. Deeper hues indicate faster current speeds while lighter hues
indicate slower current speeds. Current vectors indicate towards the direction of flow. The crest
height of the structure is set at 0.5 m above MSL so the structure will be submerged at various
portions of the tide. The emergent breakwater has a larger impact on the flood tide conditions as
seen in Figure 74. The recirculation pattern is still present on the ebb tide.
Figure 76. Calculated Currents: Emergent Breakwater Alternative
Floating Breakwater
The computed morphology change for the floating breakwater alternative is presented in
Figure 77. Warmer colors indicate accretion while cooler colors indicate erosion. Much like the
existing conditions, erosion is still present at the midpoint of the Coconut Point shoreline with a
shoal feature forming to the south west portion of the point. The location of the floating
breakwater is indicated by a red polygon.
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Figure 77. Calculated Morphology Change: Floating Breakwater Alternative
Flow patterns for the flood and ebb tide conditions are presented in Figure 78. Deeper
blues indicate faster current speeds while lighter blues indicate slower current speeds. The
floating breakwater does not significantly impact currents. The primary function of the floating
breakwater is to reduce wave heights on the lee side of the structure.
Figure 78. Calculated Currents: Floating Breakwater Alternative
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Wave heights were extracted on either side of the floating breakwater to examine the
estimated reduction in wave energy on the lee side of the structure. Wave heights on the lee side
of the structure reduced by an average of 0.8% and a segment of the time series is shown in
Figure 79. It should be noted that this analysis is limited because boat wakes were not
incorporated into the model at this time.
Figure 79. Floating Breakwater Wave Height Comparison.
Beach Fill
Different median grain sizes were used for the beach fill alternatives to examine the
effect of using larger grain size on sediment morphology at the site. Since a hard structure is not
a component in these two alternatives, flow comparisons are not included in this section.
Additional foreshore cells have been included in both of the beach fill alternatives to examine the
behavior of additional wetting and drying in the model. This more closely represents the most
likely template of a beach fill for this site.
Medium to Coarse Beach Fill
The calculated morphology change for the medium to coarse beach fill is shown in Figure
80. The median sand size used for this alternative is 1 mm. Warmer colors indicate accretion
while cooler colors indicate erosion of material. Material is deposited at the eastern and western
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
300 400 500 600 700 800 900 1000 1100 1200
Wav
e H
eigh
t (m
, MSL
)
Timestep
Floating Breakwater Alternative
Wave Height Comparison
Inshore
Offshore
111
extents of the project area but an area of erosion appears near the midpoint of the Coconut Point
shoreline.
Figure 80. Calculated Morphology Change: Beach Fill Alternative (1 mm)
Coarse Beach Fill
The calculated morphology change for the coarse beach fill is shown in Figure 81. The
median sand size used for this alternative is 4 mm. Warmer colors indicate accretion while cooler
colors indicate erosion of material. Morphology change patterns are similar for this alternative as
compared with the relatively finer grained alternative in Figure 80.
Figure 81. Calculated Morphology Change: Coarse Beach Fill Alternative (4 mm)
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Floating Breakwater with Additional Shoreface and Coarse Beach Fill
The calculated morphology change for this alternative is shown in Figure 82. Warmer
colors indicate accretion while cooler colors indicate erosion. The floating breakwater is
represented by a black polygon in the right panel. A larger volume of material is accreted on the
outer portions of Coconut Point on the lee side of the structure. Material is also accreting on the
eastern end of the point which could indicate the formation of a tombolo. A tombolo is described
in Dean, 2003 as a depositional feature created as a result of wave sheltering. Material is also
eroded at the approximate midpoint of the floating breakwater and erosion can be observed along
the length of the beach fill extents. Further alternatives for a floating breakwater could include a
structure with gaps to encourage exchange of water from the lee to seaside of the structure. Loss
of material shortly post construction is expected post construction of any beach fill.
Figure 82. Calculated Morphology Change: Floating Breakwater with Additional Shoreface and
Coarse Beach Fill Alternative
Flow conditions for both flood and ebb tide for this alternative is shown in Figure 83.
Deeper blues indicate faster current speeds while lighter hues indicate slower current
magnitudes. The configuration of the floating breakwater is shown as a black polygon and the
portion of the tide signal is shown in the inset. The breakwater has a greater reduction of current
magnitude during the ebb tide.
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Figure 83. Calculated Currents: Floating Breakwater with Additional Shoreface and Coarse Beach
Fill Alternative
8.6 Conclusion and Recommendations: Coconut Point Restoration
The dominant flow conditions do not encourage sediment migration from the flood shoal
to Coconut Point. Storms may re-suspend sediment from the flood shoal but only episodically.
Channel marginal bars may also provide sediment to Coconut Point beyond the temporal domain
of the model.
The sand trap serves as a sediment sink as intended and as a side effect reduces the
amount of sand reaching Coconut Point. The hardening of regions immediately updrift and
downdrift of Coconut Point removes the system’s natural ability to provide material to the beach
areas. Any construction alternative should combine with a regular renourishment schedule with
coarse material. The existing structures including the concrete blocks, plastic cellular material
and plastic rigid cartons should be removed. The various materials have loosened and in some
cases, are migrating. This poses a safety risk to both the public as well as the health and safety of
marine mammals, fish and birds. The removal of existing materials will also aid in the
performance of a constructed beach fill. It will be harder to predict the performance or life cycle
of a beach fill with the existing materials in place. The non-uniform erosion could occur again
after beach fill placement if the existing materials are not removed. Since the type of concrete
blocks used at the site are not commonly used in the coastal zone, their impact on
hydrodynamics is unclear. Given the severe erosion observed at the site, the concrete blocks may
be amplifying erosion in an area already devoid of sand source.
114
As part of design of a beach renourishment, a profile change model such as SBEACH
(Storm-induced BEAch CHange) should be used to evaluate the performance of the material and
help develop a renourishment schedule. SBEACH “simulates cross-shore beach, berm and dune
erosion produced by storm waves and water levels” (USACE, 2015).
115
9.0 Geographic Information Systems
Geographic Information System (GIS) in conjunction with remote sensing is the powerful and
effective tool in Coastal Management. It has been widely applied to monitor and analyze the physical and
geological change over the last decades. Remote sensing from space-borne satellites is perhaps the only
data acquisition system capable of recording many of these changes at the required spatial and temporal
resolution, given the size of the areas affected and the rate at which these changes are taking place.
(ASPRS Manual, 1981)
Modern analytical methods, including GIS based analyses, should provide more accurate
estimates of shoreline change than previous research studies due to limitations in methods and equipment
used in older studies. Compilation of historical shoreline data and maps in a geographic information
system database is critical in conducting a modern shoreline change analysis. (Langley et al, 2003) The
data including aerial images, hydrographic surveys and shoreline change can be applied to quantify the
short term and long term morphologic changes.
9.1 Sebastian Inlet Data Management
The objectives of the GIS technology in Sebastian Inlet project are to organize the available data
in a presentable format and inventorying them for the future use. The initial step is to create a digital data
set of the Sebastian Inlet into the Geographic Information Systems (GIS) technology to facilitate the
current and future shoreline change analysis. Latter is to keep them updated using the latest version of the
GIS software.
The latest version of ESRI®
software ArcGISTM has extensive capabilities to adapt the large size
data successfully. The Sebastian inlet data includes 70 years of imagery, 23 years of topographic survey
data, 30 years of Model data, 20 years of measured data i.e. waves, weather current and water level and
regional Sediment inventory. The ArcGIS®
v. 10.2.2 software has been used for various purposes such as
creating maps for the identification of the study-area, domains, to perform the geospatial analysis and
surface volume calculation.
116
Figure 84. The file Geodatabase organization in the ArcGIS® interface.
ArcGIS®
allows storing raster, vector, tables, and models in a single storage container called the File
Geodatabase which now reduces the data redundancy. It provides flexible storage of feature data set
including multiple features, data tables, images as well as model to perform analysis.
Figure 85. The morphological features presentation in the ArcMap® v 10.2.2.
Raster files
Feature class
Project files (.mxd) Feature
117
9.3 ArcGIS Spatial analysis
The ArcGIS® Spatial Analyst extension provides a wide range of powerful spatial
modeling and analysis capabilities. Users can create, query, map, and analyze cell-based raster
data; perform integrated raster or vector analysis; derive new information from existing data;
query information across multiple data layers; and fully integrate cell-based raster data with
traditional vector data sources. It allows users to perform the following functions for the coastal
analysis:
Create useful information from the available source data
Resampling or reclassifying
Surface interpolation and Surface Analysis
Perform statistical analysis based on predetermined zones.
Figure 86. The Spatial Analyst Tool box and 3D analyst Tools in the Arc Toolbox.
118
ArcGIS® provides the analyst the ability to identify the best solutions to the real world
problems in a dynamic modeling environment. The integrated tool in ArcMap® allows raster –
cell cartographic modeling. ArcGIS® spatial Analysis tool allows users to create raster data from
any points, lines or polygon features such as shape files, CAD files, images or tabular data. Users
can create outstanding display with powerful symbology and annotation. Some of the analytical
tool includes querying raster data, deriving the data, creating new surface, perform volume
change analysis.
Figure 87. Creating flood shoal surface using Kriging tool.
ESRI® ArcGIS® 3D Analyst™ provides a comprehensive array of toolsets to accomplish a wide
variety of tasks. With the ArcGIS® 3D Analyst Geo-processing tools users can create and modify
triangulated irregular network (TIN), raster, and terrain surfaces and extract information and
features from them. Moreover, the 3D Analyst toolsets allows users
Extrude two-dimensional features to three dimensions using attribute data.
To convert TINs to features and rasters
Create 3D features from functional surfaces by extracting height information;
Interpolate information from rasters
Mathematically manipulate rasters
119
Reclassify rasters; and derive height, slope, aspect, and volumetric information from
TINs and rasters
The ArcGIS® has powerful and advanced visualization, analysis, and surface generation
tools. Users can view extremely large sets of data in three-dimensions from multiple viewpoints,
query a surface, and create a realistic perspective image that drapes raster and vector data over a
surface. The following examples demonstrate the importance of integration of the modeling
capabilities with GIS.
Figure 88. Creating Surface Contour from survey point files: Use of 3D analysts tool.
120
Figure 89. Volume change analysis using cut & fill tool.
121
10.0 References
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Wamsley, T., and Zundel, A.K. 2006. Two-dimensional depth-averaged circulation model
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Camenen, B., and M., Larson. 2007. A Total Load Formula for the Nearshore. Proceedings
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Tolman, 2010: WAVEWATCH III (R) development best practices Ver. 0.1. NOAA / NWS /
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U.S Army Corps of Engineers. 2015. SBEACH – Storm-induced BEAch CHange Model.
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Wu, W., A. Sanchez, and M. Zhang. 2010. An Implicit 2-D Depth-Averaged Finite-Volume
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Changes, Local Sediment Budget and Beach Fill Performance. Sebastian Inlet Tax District,
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Processes, Historical Shoreline Changes, Local Sediment Budget and Beach Fill
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